The trouble is that, as Adrian Tinniswood shows in this endlessly entertaining book, every part of this version of events is questionable.
By 1900, the owners of large country houses were already finding it hard to maintain the large staffs necessary to run them. You may recall that Nevill Holt Hall, held by many to be the model for Bonkers Hall, had already been vacated by the Cunard family when Suffragettes tried to burn it down in 1914.
Where it remained possible to continue to operate on the 19th-century model, it was often because an American bride brought a new fortune across the Atlantic with her. There's a 1 in 20 chance that the first Lady Bonkers was American.
Death duties were indeed a heavy burden on country estates, particularly during the first world war when more than one set of them might have to be paid, but then we Liberals brought them in precisely to reduce the economic and social dominance of the landed interest.
But before 1950 the solution most houseowners came up with was to sell off part of the estate and perhaps to demolish unwanted wings of the main house - no doubt to their architectural advantage in many cases.
The worst period for country houses was the 1950s, when many were demolished after failing to find buyers. There's a Malcolm Saville story from 1958, The Secret of the Gorge, which pictures the demolition gangs moving in on a country house.
The same landscape - the Teme Gorge on the Shropshire and Herefordshire border - features in Tom Sharpe's Blott on the Landscape, as does an attempt to demolish a house. That's because both Sharpe and Saville's eldest son were pupils at Lancing, which was evacuated to Downton Castle during the war. This was another indignity that befell such houses at the time, but Downton Castle is very much still with us.
Around Market Harborough, both Gumley Hall, which became a training centre for agents to be dropped into Nazi-occupied Europe and was then home to Leonard Cheshire's first community for service veterans, and the Lutyens house Papillon Hall near Lubenham were demolished. But Nevill Holt Hall survived by becoming a prep school, which lasted until it closed following a police raid that included helicopters.
The mood of despair at the future of country houses was captured by Evelyn Waugh in Brideshead Revisited, which was published in 1945. But events moved on, and in his preface to its 1960 edition he wrote that the novel had proved "a panegyric preached over an empty coffin", but who reads prefaces?
They do watch television - or they did in 1981, when the ITV adaptation was screened. I enjoyed it, just as I enjoyed the novel when I went through a Waugh phase at university, but I have never found a more profound message in either than the thought that old money is nicer than new money.
The damage wrought upon a whole generation of Oxford-educated politicians by the TV version, however, is enormous, and the damage they have wrought upon the country as a result probably incalculable.
Yet even in the Fifties new country houses were being built, and their precursors were about to experience a revival thanks to a new phenomenon of the Sixties: the rock god. The Beatles did not live together in four knocked-through terraced houses: they had a country house each. So did several members of the Stones and the Who.
In his own quiet way, Steve Winwood is worth notice here too. He bought a Cotswold house when he was 20, in an area where only rock stars and royalty can afford to live. The result was that one of his daughters married the nephew of Camilla Parker Bowles and his grandson was one of the Queen's pages at the Coronation.
And that exhibition at the V&A? Tinniswood paints it as, in large part, an attempt to ward off Denis Healey's plans for a wealth tax. But then it's often been hard to distinguish where calls for the maintenance of the country house end and calls for the maintenance of their owners begin.
The current controversy over the National Trust, for instance, must surely be born of impatience with those of us who insist on asking awkward question about where all this affluence came from. Why can't we do the house and gardens, have a scone in the café, buy some out-of-the-way chutney in the gift shop and then leave them in peace?
With so many memoirs and diaries of upper-class eccentrics, Tinniswood had loads of enticing material and made good use of it. What I want to do now is read The Last of Uptake, a 1942 satire by Simon Harcourt-Smith that he draws on. It ends with Titmarsh the gardener burning the old pile down.
