Andrew Grice: Brown's insurance against defeat

Gordon Brown's deathbed conversion to electoral reform may look like pure opportunism and widening the goalposts for his team just as the match kicks off. But in a few months, it might just be a clever insurance policy that pays a handsome reward.

The Prime Minister's proposed referendum on the Australian-style alternative vote (AV) system for future general elections could prove a useful carrot to dangle before the Liberal Democrats in the event that the first-past-the-post contest expected on 6 May ends in a hung parliament.

AV is not a form of proportional representation, though it is often mistakenly described as such. Supporters say it is fairer than the current winner-takes-all system because every MP must – eventually – secure the support of a majority of his or her constituents. (Under AV, people rank candidates in order of preference, the bottom one drops out and second preference votes are redistributed until one gets more than 50 per cent of those voting.)

The opinion polls increasingly point to a hung parliament. A formal Lib-Con or Lib-Lab coalition is extremely unlikely. More likely is an understanding where the Liberal Democrats would support a minority Tory or Labour government in key Commons votes.

The Liberal Democrat leader, Nick Clegg, has said his actions would be guided by the people's verdict. He would not be foolish enough to prop up a dying Brown administration if David Cameron were a few seats short of an overall majority and had, in effect, "won" the election.

But the once-in-a-generation prospect of electoral reform could be quite a sweetener for the third party if the Tories and Labour won a similar number of seats. If a bigger carrot were demanded in horse-trading by the Liberal Democrats, Mr Brown might say that AV would not be the end of the reform road. He could hint at dusting down the very dusty report by the late Lord (Roy) Jenkins of Hillhead for Tony Blair in 1998, which recommended "AV plus" – with 15 or 20 per cent of MPs chosen in line with the proportion of votes cast. Electors would get two votes – one for their choice of constituency MP and the other for the top-up MP.

The Tories oppose change to the voting system. Privately, senior Liberal Democrats say they also have more in common with Labour than the Tories on other issues – when public spending cuts should start, Europe and climate change among them.

Mr Brown's move works on several levels. It demonstrates that Labour has not run out of ideas, however exhausted it may look, and has plans to reform Parliament after the MPs' expenses controversy. It potentially wrong-foots the Tories, undermining Mr Cameron's "change" message. And even if the AV referendum plan is not approved by the House of Lords before this year's election, it could be very useful for Mr Brown to have it up his sleeve if he places a call to Mr Clegg on Friday 7 May.