I have long been in favour of fixed-term parliaments, as endorsed by our new coalition government, but anyone who claims they will prevent a second election having to take place soon is wrong.

Fixed terms work well in presidential systems such as France and the United States, where the head of state's position is not dependent on the support of the legislature. But in Britain, where the executive and the legislature are merged, the Prime Minister struggles to govern if parliament turns hostile.

Jim Callaghan was forced to hold an election after his government lost a vote of no confidence in 1979. Under the Lib Dem-Tory plan, an "enhanced majority" of 55 per cent of MPs will be required to trigger a dissolution. But it's not hard to imagine the opposition plus the Tory right and the Lib Dem left joining forces to achieve just this.

And it is worth noting that, in Germany, chancellors including Helmut Kohl and Gerhard Schröder have purposely lost votes of no confidence in order to trigger an election at the most convenient moment for the government. Expect this to become a very tempting option if the government runs into trouble (as it will).

Thus, the only way to ensure genuine fixed-term parliaments is to separate the executive fully from the legislature. As a republican, I'm all in favour of this, but I fear it is still just a little too radical for this government.

Special offer: get 12 issues of the New Statesman for just £5.99 plus a free copy of "Liberty in the Age of Terror" by A C Grayling.