Nick Clegg is facing his first setback as Liberal Democrat leader, with reports suggesting that three frontbenchers will resign over tonight's vote for a referendum on the Reform Treaty.

Clegg has called on his party to abstain from Wednesday's vote on whether to hold a poll on the EU treaty.

But justice spokesman David Heath, environment spokesman Tim Farron and Scotland and Northern Ireland spokesman Alistair Carmichael are expected to defy the party whip and leave their positions.

Clegg's spokesman said no resignations had been tendered, but at least one is thought to have signed their formal resignation letter already.

Culture spokesman Richard Younger-Ross also said he would be voting for a referendum.

"My concern is, and always has been, the lack of democratic accountability and centralising nature of the EU," he said.

"I will therefore support the Reform Treaty referendum amendment as the only way to get these issues debated."