If the first rule of a political campaign is ‘never give a sucker an even break’, David Cameron has clearly failed to abide by it.

In agreeing to prime ministerial debates, Cameron gave Gordon Brown, once in a seemingly hopeless situation, the chance to revitalise his campaign. And, even if he has not made the most of it, the leader of the Liberal Democrats, Nick Clegg, has capitalised on an unprecedented opportunity for his party.By mere virtue of taking part in the debates, the Lib Dems were always going to be the winners. The chance to appear on equal footing with Labour and the Conservatives in election debates is one Paddy Ashdown or Charles Kennedy would have relished. Catapulted into the public eye like never before, the Lib Dems’ electoral aims have gone from clinging onto the 62 seats they won in 2005 to going on the offensive with theree even being talk of breaking the 100-seat barrier.

The similarities between Cameron and Tony Blair are oft remarked upon. Yet in one crucial way, Cameron failed to learn from Tony Blair. In 1997, when Blair looked as inevitable a Prime Minister as has ever existed, there was a great deal of pressure for prime ministerial debates, but Blair managed to avoid them. He simply had nothing to gain, being almost certain to win. Debates bring the candidates closer together: hence it has invariably been those trailing in the polls who have called for them.

Cameron may come to regret his performances in these debates, and, if he does not do so, see them as a key reason for his failure to win the general election. But if such a scenario manifests itself, he might reflect ruefully that, if his debating performances were less-than-perfect, the more fundamental error was his being in the debates at all.