Downton's effect on the political mood
For many, "period drama" conjures up images of Georgian ladies flouncing about in posh frocks calculating how they might marry the man of their dreams. But not all dramas set in Britain's past are escapist romantic fantasies - some may even contain veiled political messages.
This is certainly true of one of the genre's most abidingly popular strands, one which focuses on relations between the upper class and their servants.
If posh frocks are an important feature of these dramas' appeal, they also depict the laborious lives of those forced to cook and clean for those who wear them. But they present a controversial picture of the past, one that some politicians have tried to exploit.
If ITV's Downton Abbey is the most recent period drama to tackle this subject, the series has two illustrious predecessors.
During the 1970s Upstairs Downstairs beguiled millions of ITV viewers with the comings and goings at 165 Eaton Place while Noel Coward's 1931 play Cavalcade, about the Marryot household, wowed Drury Lane audiences and its 1934 Hollywood movie version was so popular it won the Oscar for best picture.
All three dramas not only had a similar interest in the master-servant relationship. They were also located in the same historical period: their three sets of characters all lived through the Edwardian summer, the horrors of World War One and the social changes that occurred during the 1920s.
The dramas also shared a similar view of how the classes related to one another, stressing the kind-heartedness of the aristocracy towards their servants. This was not too surprising given who made them. Noel Coward's origins were relatively humble but by the time of Cavalcade many of the country's elite were his friends.
The producer and script editor of Upstairs Downstairs were from very grand families - one, Alfred Shaughnessy, spoke of a Royal visit to his house.
"I remember very well when the Prince came to tea in our house. There was a feeling of Royalty coming and a little crowd outside on the pavement waiting to see the Prince drive up," said Shaughnessy.
And Downton creator Julian Fellowes says he comes from "the bottom end of the top".
So, in Cavalcade the Marryots celebrate New Year with their maid and butler and help them buy a pub when they want to leave service. In Upstairs Downstairs the Bellamy family treat their servants with respect and offer help whenever they find themselves in trouble. In Downton Abbey, despite his elevated position, Lord Grantham takes a close interest in the welfare of even the lowly kitchen maid.
As a result, one viewer told me "Lord Grantham is such a great guy. You would like to be him".
"So often he did the right thing, not necessarily what other people, other Lords in his position might have done," the viewer added.
But historians question the accuracy of this depiction, seeing it as too rose-tinted. Certainly, after their series ended, the makers of Upstairs Downstairs admitted they had deliberately presented the Bellamys in the best possible light. They had fought battles with writers like Fay Weldon who wanted to show the family in a less benign light.
All three dramas present a comforting picture, especially for the times of national crisis in which they were produced - something that might help to explain their popularity.
As Cavalcade opened, Britain was enduring the first consequences of the Wall Street Crash, which would see unemployment reach more than three million. Upstairs Downstairs was broadcast in a country buffeted by recession, the miners' strike and 25% inflation.
Downton appeared just as austerity began to bite following the 2008 financial crash.
Those who produced these dramas had various motives, to entertain being the most important but some found how they presented relations between the classes politically useful.
Viscount Rothermere, who owned the Daily Mail, believed Cavalcade had a message that would help the Conservative-dominated National Coalition win the October 1931 general election. He even asked Coward to write an article based on his play's last Act thinking it would help "rouse the people up to a very high sense of patriotism".
In 1978 Norman Tebbit and other supporters of Margaret Thatcher told her that to win office the Conservative party needed to appeal to nostalgia for a settled, civilised life and a sense of common purpose. Some critics have seen this kind of nostalgia expressed in Upstairs Downstairs.
Cameron had already become prime minister promising a "Big Society" in which everyone would pull together before Downton reached the screens. But as a "One Nation" Tory ennobled by Cameron, Julian Fellowes told me his series did have a bit of a political agenda, however slight, in as much as it depicted those from different backgrounds caring for one another.
"I think that I had one bit of political agenda, if I'm completely honest, in that I am a One Nation Tory and I dislike the way politicians encourage us to hate each other in order to engender votes."
We will never know for sure how far these dramas altered their audiences' political beliefs, and I am wary of ascribing motives to those who wrote them, bearing in mind the warning that Coward himself made about searching for his reasons for writing Cavalcade.
"Some people make a career of motive discovery, they search every word for a clue, like old ladies peering under the bed for burglars," said Coward.
But these dramas certainly contain a socially conservative message, which suggests that despite our class differences the British form part of One Nation, the members of which are - especially in the midst of crisis - "All in It Together" and in which the top will look after the bottom.
It's a comforting message, one that has sent millions to bed in a happier state of mind. But it's largely based on a myth, one that bears little relationship to the country's actual past.
Perhaps this is only a matter of concern for historians but if these dramas don't say anything about Britain as it actually was they do suggest much about how many would like it to have been.
Archive on 4: Period Drama Politics TX on Saturday 10 September at 20.00 on Radio 4.