Britain could face a crisis which pushes it out of the European Union, Deputy Prime Minister Nick Clegg said today.

"You will never achieve (anything) by stamping your foot and saying 'well we want to be part of this club, we want to unilaterally rewrite the rules of the games and we want to pick and choose unilaterally what we sign up to,'" said Clegg, the leader of the pro-European Liberal Democrats.

"My worry is that it is a much shorter leap from that to an outright crisis which would leave the United Kingdom fully marginalised or even out of the European CLEGGon than people seem to imagine," Clegg said.