Mycroft the Enigma Part 2 - Holmes Family Fortunes
A genuinely brilliant ask from Annoymous that I managed to delete by accident: “How rich do you think Mycroft Holmes is?”
I delve into the Holmes Family background, explore the Holmes ancestral mansion (as seen in ASiB) and a history of the gentry. I speculate as to Mycroft's professional salary and where his wealth comes from.
Canon Considerations
In the ACD adventures very little is said about the socio-economic status of the Holmes family. However it was clear to readers at the time that Sherlock Holmes was definitely middle class, perhaps even upper middle class give his brother’s position within the government. In the Victorian era, a career in the government required connections - very few working class/lower middle class politicians or senior civil servants existed in this era. Politicians did not start receiving a salary until the very end of the 19th century. Senior members of the government nearly all belonged to the “Old Boy’s Club”.
Thanks to the knowledge of thenorwoodbuilder: I have been reliably informed that Sherlock states "My ancestors were country squires, who appear to have led much the same life as is natural to their class" and mail for Holmes is usually addressed to “Sherlock Holmes, Esq.”
Esquires are a class of gentry.
The upper class of Britain is separated into two distinct sectors: the peerage and the gentry. A peerage is a hereditary title (e.g. Duke, Earl, and Viscount) conferred by the monarch on a favoured subject and is usually only passed on to the eldest son. The rest of their offspring may inherit money/land/prestige but not the actual title. These younger children and their descendent are the historical origins of the term "gentry".
Esquire is used to denoted someone of high but indeterminate social status. Esquires are considered gentlemen without titles and can either be descendent of self-made men or the cadet branches of families holding peerages. Esquire is not a title and anyone who can afford the lifestyle and social graces of the landed gentry can adopt this term. As it is not a formal title: there are no rules about inheritance. All the sons of an Esquire can be Esquires.
Therefore the Holmes Family may come from a distinguished line of ancient nobility or could be comparatively new upstarts who had to buy their own furniture.
I am more inclined to believe that the Holmes Family in ADC was supposed to be a cadet branch of a minor aristocratic family: unremarkable but with the right kind of background for rising up in the government as Mycroft Holmes did.
Minor country gentry have land holdings but their size varies enormously. Some may own more land than minor peers of the realm, whilst others have hardly enough to support themselves with. The (comparatively) penniless aristocrat is a common figure thought history and is particularly common in the Victorian Era when fortunes were made in industry not agriculture.
Given Sherlock and Mycroft’s general lack of concern for their finances, we can assume that their land holdings provide a steady stream of revenue. With the invention of stocks and shares in the 18th century, shrewd investment may also be a source of wealth for the landed gentry.
Money in the Modern Day
So how does all of this translate to BBC Sherlock?
There is no reason to believe that the Holmes Family in BBC Sherlock are not still “minor country gentry”. The existence of the house where Mycroft spends Christmas supports such an idea. As does Mycroft’s wardrobe (which does not come cheap) and Sherlock’s general lack of concern for money.
If, as the writers intended, Mycroft and Sherlock were merely transplanted in the modern era, how rich would they be?
In past centuries, unlike the peerage, landed gentry are not compelled to leave most/all of their fortune to the eldest son in order to support the title they have inherited. Instead they are quite free to divide their land holdings/money equally between the sons upon the death of the father (daughters get dowries when they marry). However this typically produces smaller and smaller land holdings, until they become impossible to support the lifestyle expected by the gentry.
Mycroft appears to be wealthy but Sherlock has to share the flat he rents and given his general distain for the rest of humanity I doubt this is purely by choice. I think it is more likely that Mycroft inherited the bulk of the family holdings, whereas Sherlock received some money/other forms of liquid assets.
Amendment- Regarding Sherlock: Property is difficult to divide, simply because you can't split a country estate down the middle for two sons. Additionally precedent for primogenture may have been set in law for this particular family several generations back to avoid the splitting up of the Holmes estate (a common type of contract amongst the aristocracy). Thus Mycroft's parents may have had no legal option but to leave him the entire estate and all their assets, giving only liquid currency to Sherlock. As with most aristocractic families in the modern day: their assests significantly outweight their cash. Therefore by default Mycroft inherits the solid assets which he cannot liquidate but will generate a large income over time, whereas Sherlock gets a lump sum of cash.
There is no evidence that Sherlock's parents set up a trust fund for their son to manage his lump sum of cash, it might not have been worth their while. We have no idea how much cash/liquid assets they even had to bequeath to Sherlock. Cash inheritences are taxed very quickly because unlike property you cannot delay paying the inheritence tax and therefore spread your loss over time (as Mycroft could have done). Inheritence tax in the UK runs up to 50% and thus even if the Holmes left their second son a considerable amount, when he actually got hold of the money there might not be much left.
Having a trust fund would not bode well for the brothers' relationship. Sherlock is highly independent and he would be very unhappy to have his inheritence controlled by Mycroft. As a fully competent adult Sherlock has the legal right to manage his own financial affairs. He is also fully entitled to challenge Mycroft's trusteeship of his trust fund if he feels that as the beneficiary, he is suffering from the relationship or that Mycroft is deliberately abusing his position. No parent wants their children to end up fighting each other in court and the outcome hardly matters if your family name and something as private as your finances are dragged out into the open to be scrutinised by lawyers.
It would have simply been easier to leave some money to Sherlock but give it to him directly. Mycroft would have the bulk of the assets, the Holmes Family are assured that their main holdings remain in the hands of a capable manager. They must have instruct Mycroft to provide for his younger brother, and trusted that this would be carried out one way or another. Sherlock cannot take Mycroft to court for giving him money - the worst he can do is simply refuse to accept it, which is probably why he's living with a flatmate at the moment despite being a very private man.
Where does Mycroft get his Money From?
If we start by looking at his day job (Mycroft the Engima Part 1) as a senior civil servant - Mycroft’s official salary is within the range of £70,000 - £100,000.
This sounds like luxurious enough wage for friends across the Atlantic in the US but I would like to remind all fanfiction writers that taxes in Britain are much higher than in the US/Canada. We have a National Health Service and much larger welfare spending compared with the US.
Putting all the possible taxes we pay together (National Insurance, Income tax, council tax, road tax, VAT, petrol tax) someone earning over £100,000 would most likely only get to keep 30% - 40% of their actual salary. This is not all disposable income, you need to factor things like rent/mortgage, food, gas and electricity into the equation.
Thus we live in a country where the more you earn on paper the less you end up getting to take home. This is why most doctors do not want engage in purely private practice because it is not more profitable than working on the NHS and you don’t get the benefits of a state pension.
I doubt Mycroft is able to keep up the appearances he gives on camera on his senior civil servant’s wage alone. Although the sleek black cars and the professional drivers may be a perk of his job - I still don’t think he would manage to retain a country house (seen in ASiB) in habitable order and potentially a London residence at the same time.
Please remember that unlike MPs who can claim expenses such as rent and council tax back from the government for their London homes, civil servants have no such privileges. They also have very few perks of the job, most senior civil servants are not even given a government car, though I assume Mycroft has one.
Of course Mycroft can engage in the age old art of tax-avoidance which as Starbucks will tell you is not illegal. He can exploit loop holes in the law and pay substantially less tax than everyone else. However there are repercussions. Firstly, tax-avoidance can be traced - Google and Starbucks have come under fire after their schemes were discovered. Secondly, as unofficial consulting "disaster manager" Mycroft requires the good will of the government departments he works with. He does not have the right to impose himself on various departments because his position as consulting "disaster manager" is unofficial. He needs to remain above approach to prevent detractors from getting in the way of his work. Although he is a private citizen, unlike MPs, he still trades upon his reputations within government for his career.
His inheritance is probably the key to his current wealth. As I’ve said before Mycroft inherited the bulk of the family fortune (although it might have only been a small fortune).
A Brief History of Homes
Speaking of family fortune, I would like to point out that the Holmes country estate is either in London or just outside it because Mycroft was able to rush back into Central London to see his brother in the morgue during Christmas night.
Having a country house inside London is not inconceivable. The city we know today is about twice as large (in geographical terms) as it was in the 1850s. This means that minor country houses in the Victorian Era could have been swallowed up by sprawl of modern London.
(London c. 1850 - if you look in south of the river Thames, most of the development has yet to happen)
London’s development might have contributed greatly to the Holmes family wealth. They would not have been the first landowner to profit from property development. Instead of selling the land, they might have retained the freehold (i.e leased the land to the house owners for a flat yearly fee). In this fashion, Mycroft may still be accruing payments from hundreds if not thousands of leasehold properties every year.
If the Holmes family had been shrewd they might have gone into property development in the pre-war and post-war periods - so not only do they own the land, they may also still own swaths of suburban housing upon which they could have built an extensive property portfolio.
Given how house prices (and consequently rent prices) have risen in London in the last two decades, if Mycroft does control a property portfolio his wealth would have double/tripled by the time the series starts in 2010. Britain is still in the middle of an economic crisis but house prices haven't significantly fallen (mostly because the government hasn't approved enough land for property development).
However we need to take into account the Holmes ancestral house. Country houses are eye-wateringly expensive to run, particularly a late medieval/Tudor (c.1400 - 1600) one we see Mycroft spending Christmas in. Most large country houses were turned over to the National Trust in the post-war period (c. 1945 - 1960) when Labour introduced heavy taxation to fund the welfare state and rebuilding of the nation. The ones that stayed in private hands are now also open to the public (see Chatsworth House/Blenheim Palace) and earn their keep as tourist destinations/wedding venues.
We have no evidence that Mycroft has turned his private mansion into a tourist trap. Therefore he must be making sufficiently large sums of money to maintain his ancestral home.
Other Potential Sources of Revenue
We have no reason to believe the Holmes family were rich in assets but poor in liquid capital. They might have thriving business empire going and all Mycroft really has to do is sit back and watch the money flow. This may be why he is completely free to indulge his patriotic duty and build his own power base.
(Side note - Mycroft the Patriot:
I find it very difficult to read fanfiction wherein Mycroft selfishly further his own ends at the expense of his country. It is human nature to want power and I do not think that Mycroft has a mental disorder regarding power/control. He is genius, even more so than his brother and yet he chooses to undertake a dangerous, stressful position for which he will never receive official gratitude or acknowledgement. There are so many more ways to become powerful - in business, politics or the military. These are at least legitimate, recognised avenues with big rewards for the victor. In the same way Mycroft asks John, we must ask ourselves: “he has the brain of scientist or philosopher and yet he chooses to dedicate himself to protection of his country, what can we deduce about his heart?”
We used to sing “I vow to thee my country” in school and I wonder if Mycroft lives his life by this hymn? I recommend readers youtube it - whether you agree with the lyrics, it is still a beautiful song)
Additionally, with capital comes investment: stocks, shares, bonds etc. I doubt Mycroft manages his wealth himself - it is much better to have an expert do so.
If I am wrong and the Holmes family fortune amounted to nothing more than their country house (in a state of disrepair), I imagine it would not have been particularly hard for a man of Mycroft’s intellect to turn his small amount of capital into a fortune through shrewd investment.
Another route to financial success is to make use of his government knowledge and connections. I am not saying that the British Government is corrupt, although elements of corruptions exist in every system. However, Mycroft as civil servant would have an accurate understanding of legislation regarding investments, property development, business setup etc. It is much easier to navigate the maze of red tape if you’re the one who built it in the first place. He may not be using insider knowledge or insider trading; he would merely be better positioned to understand which direction the government is heading. For example: the past Labour government liked wind farms and approved many projects but the current Conservative government is not so keen and thus companies who specialise in renewable energy have suffered in the UK.
Side Note - Why does Mycroft have a Horse in His Dining Room?
Mycroft Holmes doesn’t have a horse in his dining room - he has a set of matching statues of "knights" on horseback. Their head dress appear to be somewhat exotic but otherwise I cannot tell much else about them. They may have been collected during the days of the British Empire when it was a fad to plunder the provinces (and Europe) for collectables.
The room is also not the dining room. If you look closely at the chairs you will see that it’s the same room that Mycroft, Sherlock and Irene have their “discussion” at the end of ASiB. It is also the same room where Mycroft answers the phone from Sherlock at Christmas.
Dining rooms in country houses are just dining rooms - they do not usually contain other pieces of furniture such as couch/armchairs. It is a status symbol to have room dedicated only to eating meals. Given how little time we spend eating compared to everything else - it shows you have space to spare.
You don’t want to put unnecessary soft upholstery in the dining room, in case the smell of food becomes encased in the fabric (this is in the era before air fresheners existed).
The room we see in ASiB is definitely either a drawing room or a sitting room for the family. It is not part of the state rooms of the house where important visitors would be shown to - it is more likely to be used solely for the family hence the dual purpose of the room. I’m sure Mycroft might have his dinner in there but it is not his dining room.
Given the size and architecture - I think it is a remnant of the great hall (in a small country house they are usually not very big) that all late medieval/Tudor grand houses had. The Georgian and Victorian styles of living had no use for this archaic room and therefore it was converted into all sorts of different types of rooms.
Other Parts in the Series:
Mycroft the Enigma Part 1 - James Bond was a Civil Servant too...
Irene's Royal Flush
Checkmate Endgame
I delve into the Holmes Family background, explore the Holmes ancestral mansion (as seen in ASiB) and a history of the gentry. I speculate as to Mycroft's professional salary and where his wealth comes from.
Canon Considerations
In the ACD adventures very little is said about the socio-economic status of the Holmes family. However it was clear to readers at the time that Sherlock Holmes was definitely middle class, perhaps even upper middle class give his brother’s position within the government. In the Victorian era, a career in the government required connections - very few working class/lower middle class politicians or senior civil servants existed in this era. Politicians did not start receiving a salary until the very end of the 19th century. Senior members of the government nearly all belonged to the “Old Boy’s Club”.
Thanks to the knowledge of thenorwoodbuilder: I have been reliably informed that Sherlock states "My ancestors were country squires, who appear to have led much the same life as is natural to their class" and mail for Holmes is usually addressed to “Sherlock Holmes, Esq.”
Esquires are a class of gentry.
The upper class of Britain is separated into two distinct sectors: the peerage and the gentry. A peerage is a hereditary title (e.g. Duke, Earl, and Viscount) conferred by the monarch on a favoured subject and is usually only passed on to the eldest son. The rest of their offspring may inherit money/land/prestige but not the actual title. These younger children and their descendent are the historical origins of the term "gentry".
Esquire is used to denoted someone of high but indeterminate social status. Esquires are considered gentlemen without titles and can either be descendent of self-made men or the cadet branches of families holding peerages. Esquire is not a title and anyone who can afford the lifestyle and social graces of the landed gentry can adopt this term. As it is not a formal title: there are no rules about inheritance. All the sons of an Esquire can be Esquires.
Therefore the Holmes Family may come from a distinguished line of ancient nobility or could be comparatively new upstarts who had to buy their own furniture.
I am more inclined to believe that the Holmes Family in ADC was supposed to be a cadet branch of a minor aristocratic family: unremarkable but with the right kind of background for rising up in the government as Mycroft Holmes did.
Minor country gentry have land holdings but their size varies enormously. Some may own more land than minor peers of the realm, whilst others have hardly enough to support themselves with. The (comparatively) penniless aristocrat is a common figure thought history and is particularly common in the Victorian Era when fortunes were made in industry not agriculture.
Given Sherlock and Mycroft’s general lack of concern for their finances, we can assume that their land holdings provide a steady stream of revenue. With the invention of stocks and shares in the 18th century, shrewd investment may also be a source of wealth for the landed gentry.
Money in the Modern Day
So how does all of this translate to BBC Sherlock?
There is no reason to believe that the Holmes Family in BBC Sherlock are not still “minor country gentry”. The existence of the house where Mycroft spends Christmas supports such an idea. As does Mycroft’s wardrobe (which does not come cheap) and Sherlock’s general lack of concern for money.
If, as the writers intended, Mycroft and Sherlock were merely transplanted in the modern era, how rich would they be?
In past centuries, unlike the peerage, landed gentry are not compelled to leave most/all of their fortune to the eldest son in order to support the title they have inherited. Instead they are quite free to divide their land holdings/money equally between the sons upon the death of the father (daughters get dowries when they marry). However this typically produces smaller and smaller land holdings, until they become impossible to support the lifestyle expected by the gentry.
Mycroft appears to be wealthy but Sherlock has to share the flat he rents and given his general distain for the rest of humanity I doubt this is purely by choice. I think it is more likely that Mycroft inherited the bulk of the family holdings, whereas Sherlock received some money/other forms of liquid assets.
Amendment- Regarding Sherlock: Property is difficult to divide, simply because you can't split a country estate down the middle for two sons. Additionally precedent for primogenture may have been set in law for this particular family several generations back to avoid the splitting up of the Holmes estate (a common type of contract amongst the aristocracy). Thus Mycroft's parents may have had no legal option but to leave him the entire estate and all their assets, giving only liquid currency to Sherlock. As with most aristocractic families in the modern day: their assests significantly outweight their cash. Therefore by default Mycroft inherits the solid assets which he cannot liquidate but will generate a large income over time, whereas Sherlock gets a lump sum of cash.
There is no evidence that Sherlock's parents set up a trust fund for their son to manage his lump sum of cash, it might not have been worth their while. We have no idea how much cash/liquid assets they even had to bequeath to Sherlock. Cash inheritences are taxed very quickly because unlike property you cannot delay paying the inheritence tax and therefore spread your loss over time (as Mycroft could have done). Inheritence tax in the UK runs up to 50% and thus even if the Holmes left their second son a considerable amount, when he actually got hold of the money there might not be much left.
Having a trust fund would not bode well for the brothers' relationship. Sherlock is highly independent and he would be very unhappy to have his inheritence controlled by Mycroft. As a fully competent adult Sherlock has the legal right to manage his own financial affairs. He is also fully entitled to challenge Mycroft's trusteeship of his trust fund if he feels that as the beneficiary, he is suffering from the relationship or that Mycroft is deliberately abusing his position. No parent wants their children to end up fighting each other in court and the outcome hardly matters if your family name and something as private as your finances are dragged out into the open to be scrutinised by lawyers.
It would have simply been easier to leave some money to Sherlock but give it to him directly. Mycroft would have the bulk of the assets, the Holmes Family are assured that their main holdings remain in the hands of a capable manager. They must have instruct Mycroft to provide for his younger brother, and trusted that this would be carried out one way or another. Sherlock cannot take Mycroft to court for giving him money - the worst he can do is simply refuse to accept it, which is probably why he's living with a flatmate at the moment despite being a very private man.
Where does Mycroft get his Money From?
If we start by looking at his day job (Mycroft the Engima Part 1) as a senior civil servant - Mycroft’s official salary is within the range of £70,000 - £100,000.
This sounds like luxurious enough wage for friends across the Atlantic in the US but I would like to remind all fanfiction writers that taxes in Britain are much higher than in the US/Canada. We have a National Health Service and much larger welfare spending compared with the US.
Putting all the possible taxes we pay together (National Insurance, Income tax, council tax, road tax, VAT, petrol tax) someone earning over £100,000 would most likely only get to keep 30% - 40% of their actual salary. This is not all disposable income, you need to factor things like rent/mortgage, food, gas and electricity into the equation.
Thus we live in a country where the more you earn on paper the less you end up getting to take home. This is why most doctors do not want engage in purely private practice because it is not more profitable than working on the NHS and you don’t get the benefits of a state pension.
I doubt Mycroft is able to keep up the appearances he gives on camera on his senior civil servant’s wage alone. Although the sleek black cars and the professional drivers may be a perk of his job - I still don’t think he would manage to retain a country house (seen in ASiB) in habitable order and potentially a London residence at the same time.
Please remember that unlike MPs who can claim expenses such as rent and council tax back from the government for their London homes, civil servants have no such privileges. They also have very few perks of the job, most senior civil servants are not even given a government car, though I assume Mycroft has one.
Of course Mycroft can engage in the age old art of tax-avoidance which as Starbucks will tell you is not illegal. He can exploit loop holes in the law and pay substantially less tax than everyone else. However there are repercussions. Firstly, tax-avoidance can be traced - Google and Starbucks have come under fire after their schemes were discovered. Secondly, as unofficial consulting "disaster manager" Mycroft requires the good will of the government departments he works with. He does not have the right to impose himself on various departments because his position as consulting "disaster manager" is unofficial. He needs to remain above approach to prevent detractors from getting in the way of his work. Although he is a private citizen, unlike MPs, he still trades upon his reputations within government for his career.
His inheritance is probably the key to his current wealth. As I’ve said before Mycroft inherited the bulk of the family fortune (although it might have only been a small fortune).
A Brief History of Homes
Speaking of family fortune, I would like to point out that the Holmes country estate is either in London or just outside it because Mycroft was able to rush back into Central London to see his brother in the morgue during Christmas night.
Having a country house inside London is not inconceivable. The city we know today is about twice as large (in geographical terms) as it was in the 1850s. This means that minor country houses in the Victorian Era could have been swallowed up by sprawl of modern London.
(London c. 1850 - if you look in south of the river Thames, most of the development has yet to happen)
London’s development might have contributed greatly to the Holmes family wealth. They would not have been the first landowner to profit from property development. Instead of selling the land, they might have retained the freehold (i.e leased the land to the house owners for a flat yearly fee). In this fashion, Mycroft may still be accruing payments from hundreds if not thousands of leasehold properties every year.
If the Holmes family had been shrewd they might have gone into property development in the pre-war and post-war periods - so not only do they own the land, they may also still own swaths of suburban housing upon which they could have built an extensive property portfolio.
Given how house prices (and consequently rent prices) have risen in London in the last two decades, if Mycroft does control a property portfolio his wealth would have double/tripled by the time the series starts in 2010. Britain is still in the middle of an economic crisis but house prices haven't significantly fallen (mostly because the government hasn't approved enough land for property development).
However we need to take into account the Holmes ancestral house. Country houses are eye-wateringly expensive to run, particularly a late medieval/Tudor (c.1400 - 1600) one we see Mycroft spending Christmas in. Most large country houses were turned over to the National Trust in the post-war period (c. 1945 - 1960) when Labour introduced heavy taxation to fund the welfare state and rebuilding of the nation. The ones that stayed in private hands are now also open to the public (see Chatsworth House/Blenheim Palace) and earn their keep as tourist destinations/wedding venues.
We have no evidence that Mycroft has turned his private mansion into a tourist trap. Therefore he must be making sufficiently large sums of money to maintain his ancestral home.
Other Potential Sources of Revenue
We have no reason to believe the Holmes family were rich in assets but poor in liquid capital. They might have thriving business empire going and all Mycroft really has to do is sit back and watch the money flow. This may be why he is completely free to indulge his patriotic duty and build his own power base.
(Side note - Mycroft the Patriot:
I find it very difficult to read fanfiction wherein Mycroft selfishly further his own ends at the expense of his country. It is human nature to want power and I do not think that Mycroft has a mental disorder regarding power/control. He is genius, even more so than his brother and yet he chooses to undertake a dangerous, stressful position for which he will never receive official gratitude or acknowledgement. There are so many more ways to become powerful - in business, politics or the military. These are at least legitimate, recognised avenues with big rewards for the victor. In the same way Mycroft asks John, we must ask ourselves: “he has the brain of scientist or philosopher and yet he chooses to dedicate himself to protection of his country, what can we deduce about his heart?”
We used to sing “I vow to thee my country” in school and I wonder if Mycroft lives his life by this hymn? I recommend readers youtube it - whether you agree with the lyrics, it is still a beautiful song)
Additionally, with capital comes investment: stocks, shares, bonds etc. I doubt Mycroft manages his wealth himself - it is much better to have an expert do so.
If I am wrong and the Holmes family fortune amounted to nothing more than their country house (in a state of disrepair), I imagine it would not have been particularly hard for a man of Mycroft’s intellect to turn his small amount of capital into a fortune through shrewd investment.
Another route to financial success is to make use of his government knowledge and connections. I am not saying that the British Government is corrupt, although elements of corruptions exist in every system. However, Mycroft as civil servant would have an accurate understanding of legislation regarding investments, property development, business setup etc. It is much easier to navigate the maze of red tape if you’re the one who built it in the first place. He may not be using insider knowledge or insider trading; he would merely be better positioned to understand which direction the government is heading. For example: the past Labour government liked wind farms and approved many projects but the current Conservative government is not so keen and thus companies who specialise in renewable energy have suffered in the UK.
Side Note - Why does Mycroft have a Horse in His Dining Room?
Mycroft Holmes doesn’t have a horse in his dining room - he has a set of matching statues of "knights" on horseback. Their head dress appear to be somewhat exotic but otherwise I cannot tell much else about them. They may have been collected during the days of the British Empire when it was a fad to plunder the provinces (and Europe) for collectables.
The room is also not the dining room. If you look closely at the chairs you will see that it’s the same room that Mycroft, Sherlock and Irene have their “discussion” at the end of ASiB. It is also the same room where Mycroft answers the phone from Sherlock at Christmas.
Dining rooms in country houses are just dining rooms - they do not usually contain other pieces of furniture such as couch/armchairs. It is a status symbol to have room dedicated only to eating meals. Given how little time we spend eating compared to everything else - it shows you have space to spare.
You don’t want to put unnecessary soft upholstery in the dining room, in case the smell of food becomes encased in the fabric (this is in the era before air fresheners existed).
The room we see in ASiB is definitely either a drawing room or a sitting room for the family. It is not part of the state rooms of the house where important visitors would be shown to - it is more likely to be used solely for the family hence the dual purpose of the room. I’m sure Mycroft might have his dinner in there but it is not his dining room.
Given the size and architecture - I think it is a remnant of the great hall (in a small country house they are usually not very big) that all late medieval/Tudor grand houses had. The Georgian and Victorian styles of living had no use for this archaic room and therefore it was converted into all sorts of different types of rooms.
Other Parts in the Series:
Mycroft the Enigma Part 1 - James Bond was a Civil Servant too...
Irene's Royal Flush
Checkmate Endgame