How the present parliament has seen the least stable Cabinet

That British governments are reshuffled too often, and that ministers spent too little time in one job, has becone a sine qua non of British politics.

There have been 5 Chief Secretary's in the 2005 parliament - more than in any parliament in the last 40 years (NewLabours first parliament, 1997-2001 is the only rival with 4 in 4 years).
4 Trade Secretaries (Thatcher had 4 in 1983-1987, but most parliaments have had 3- - still an average turnover of a new one about every 15th months).
4 Defence Secretaries (only the Falklands Parliament of 1979 has come close with 3, most of had 2).
4 Home Secretaries (the 1987 parliament had 3, but all the others since 1970 have had 2 or, occasionally, just 1)

Of the 10 senior (and for this sort of exercise importantly, reasonably consistent as Cabinet jobs across the period), only Agriculture (hardly a priority post for either party) has had fewer incumbents in the 2005 parliament than any other 1970- parliament.

But comparisons over a longer term don't show a higher turnover. Compare the 13 years from 1979-1992 (Conservative government, bookended by elections and with a change of Prime Minister towards the end) and from 1997-2010 (ditto, aside from obviously being a Labour government) and you'll find remarkably similar turnover rates.

There were 7 Tory defence secretaries, 6 for Labour. 5 Home Secretaries for the Conservatives, 6 for Labour. 6 (Con) and 4 (Lab) in the Foreign Office, 5 and 6 for Education and for Health, 10 and 8 for Trade, 4 and 5 for Agriculture, and 4 and 2 for the Chancellor and 7 and and 10 for his deputy, the Chief Secretary. Only Local Government shows any significant divergence between the two governments - 9 Secretaries of State (for Environment) under the Tories and just 5 for Labour (though the department they headed changed almost as often as they did).

What does all this tell us? It tells us that, apart from this Parliament, turnover in the top jobs of British politics has been reasonably stable since 1970. It tells us that the Trade Secretary post, having been held by both Mandelson and Heseltine potentially the most important post after the traditional great-3-offices-of-state has by far the highest turnover of heads of department. That the defence post hasn't turned into a game of musical chairs under Labour. And that the Environment Secretary post under the Conservatives changed hands much more often that (at least I) imagined.

Spreadsheet at www.mapsstatsandpolitics.talktalk.net/Turnover.xls