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Yesterday's announcement by the former Conservative deputy leader Michael Ancram that he is standing down at the next election is only the latest example of a highly significant trend.

The ´óÏó´«Ã½'s Political Research Unit now reckons there are 102 MPs now retiring at the next election.

Since 1945 the record number of MPs to retire at any election was 117 in 1997.

The Conservative Party Chairman Eric Pickles predicted last week that roughly 17 more Tories would retire because of the expenses scandal.

I would estimate the number of retirements yet to be announced on the Labour side to be between 30 and 40, partly because there are almost twice as many Labour MPs as Tories, and partly because many expect to lose their seats (so why go through the agony and humiliation). The Labour whips are said to think it could be many more.

Two MPs who have not yet announced their retirements - one Labour minister, one prominent Conservative backbencher - have already confided to me over lunch that they plan to do so in due course.

If you add a few more Liberal Democrats, Irish and other MPs then we could easily be heading for 140 to 150 retirements at the next election - maybe more. Some think the figure could reach 200.

That's almost a quarter of the whole House, and a higher figure even than in 1945, when there hadn't been a general election for ten years.

The figures below set out how many MPs have retired at each election since the war:

The different figures partly reflect the length of each Parliament, of course, so one would expect more MPs to retire after a 5-year Parliament than after a 4-year one (as in 2005).

An interesting trend is that in recent years the number of retirements has gradually increased. Since 1970, only one general election has seen fewer than 70 MPs retire - 1979 when 61 MPs stepped down (and October 1974 which was the second election in eight months). But before 1970 the highest figures were 66 in both 1950 and 1966.

Why this trend? Partly because local parties increasingly expect their MPs to retire at around the state retirement age rather than hang on into their 70s and 80s. The result is that far fewer MPs leave the Commons these days by death mid-term causing by-elections.

The increased number of retirements may also reflect the fact that MPs work a lot harder than they used to. You can no longer get away with being an MP who is semi-retired, as Winston Churchill did, for example, for his last nine years as an MP.

An added reason for MPs retiring at the next election, on top of the expenses scandal, and the prospect of defeat, may be the increasing restriction on outside employment, and the new requirements for MPs to declare such earnings publicly. Howard Stoate gave his desire to continue his outside work as a GP as a reason why he is stepping down (though he was pretty likely to lose his seat anyway).

And there are the points Alan Duncan made in the surreptitiously recorded video released today: "you have to live on rations and you are treated like shit".

So what are the political implications of all this?

Well, there will be a lot of fresh blood in Parliament, youngsters with fresh ideas and a different outlook, less stuck in the old ways of doing politics. On the other hand we may also have a House of Commons which is a lot less willing to challenge the government. New MPs tend not to rebel or ask awkward questions until they have built up experience and lost hope of achieving ministerial office. And there will also be far fewer old lags around the House who know how to cause trouble.

Which will all be good news, I suspect, for David Cameron.