Sir Menzies Campbell will either be sacked or will end up in the Cabinet

There is just one consolation for Sir Menzies Campbell as he prepares for his second and probably last conference as Liberal Democrat leader: they will not come after him in Brighton. It is too late, now, to knife the leader. Gordon Brown could call an election at any moment, and there is no time for regicide. Sir Menzies has been saved by the sheer desperation of his predicament.

So much fun has been had blaming David Cameron for Labour’s lead in the opinion polls that few have looked closely at where Mr Brown’s new voters are really coming from. The Conservatives have, in fact, held on to their voters reasonably well. The Lib Dems, by contrast, have suffered an exodus. For years, the Lib Dem party has been used as a left-wing sanctuary for voters who could not stomach Tony Blair. Now he has gone, they are returning to the Labour fold.

If today’s polls were tomorrow’s election results, Sir Menzies would be leading his troops into a massacre — from 63 seats to just 35, according to the latest YouGov research. That would be the sharpest retreat since Jeremy Thorpe lost half the Liberal party’s seats in June 1970. Such a prospect will give extra fervour to the Lib Dem prayer groups which normally start each day’s conference meeting: the end may indeed be nigh.

By no means all of this is Sir Menzies’s fault. At the last election, his party was alone in campaigning on the environment and against the Iraq war. Now the Conservative party logo is a fuzzy green tree, and the Iraq debate is now simply about when to withdraw troops from Basra. The Lib Dems have remained ideologically steady, while others have changed.