The European question (pro or contra? in or out?) has divided the main parties for decades. The Tories’ internal convulsions over Europe led to the downfall of Margaret Thatcher and tore the party apart under John Major. Labour grappled with divisions on the issue in the ’70s and ’80s.

But last night, it was the pro-European Lib Dems who appeared to have fallen prey to the political curse that is Europe.

Nick Clegg’s order to his MPs to abstain on a vote on whether to hold a referendum on the new European Union treaty left his party in disarray and a question mark over his leadership, less than three months into the post.

Labour was hit by a smaller rebellion than it could have been and the Conservatives managed to put on a show of unity with just a few exceptions — but a quarter of Lib Dem MPs defied Clegg and three frontbenchers had to resign.

It’s an embarrassing outcome for a party that has been the most consistently pro-European for years and should have been the most united on the issue.

“He sat on the fence as a point of principle,” mocked Conservative MP Theresa May in the Commons on Thursday.

The outcome leaves Clegg looking vulnerable as he goes into his party’s spring conference in Liverpool this weekend and the trouble isn’t over yet in parliament. Lib Dem Lords may defy him on the same vote in the upper chamber. And a Lib Dem abstention in the Lords could force another vote in the Commons on the same issue, presenting Clegg and pro-referendum MPs with the same quandary.

There is little sense in the Commons that the Lib Dems have a taste for yet another leadership race so early into Clegg’s tenure.

Clegg’s faux pas, however, may have left some Lib Dems scratching their heads as to why they didn’t stick with Vince Cable following the ousting of Menzies Campbell. Caretaker Cable’s challenges to Brown over Northern Rock hit the mark and his joke on Gordon Brown’s “remarkable transformation in the last few weeks from Stalin to Mr Bean” will not be forgotten.

But Clegg’s stumble means he needs to prove himself even more than before. He has yet to make a real mark in prime minister’s questions or on any particular policy.

And the Lib Dems are losing their trump card with the voters — Iraq. Their opposition to the war won sympathy with many in past years and gave anti-war Labour voters an option. But as Iraq drops down the agenda, the Lib Dems and Clegg need to find new impetus. The Liverpool conference will be a test, as will the May local elections.