David Cameron's EU referendum promise is "not in the national interest" and risks derailing the fragile UK economy, Deputy Prime Minister Nick Clegg has warned.
He launched a renewed assault on his coalition partner as several opinion polls suggested the Tories had reaped an opinion poll bounce from the long-awaited policy.
Mr Cameron insists he wants to stay in the EU but pledged to claw back powers and offer voters a choice of new relationship or exit by the end of 2017 if the Conservatives are returned to power in 2015.
It has delighted eurosceptic backbenchers fearful of the challenge of the UK Independence Party which slipped back in the latest polls after a recent surge.
Mr Clegg dismissed the prospects of securing a significant renegotiation and suggested Mr Cameron should be concentrating on the economy - which risks slumping into a triple-dip recession.
"My priority will always remain a simple objective of building a stronger economy in a fairer society, enabling everybody to get on in life," the Liberal Democrat leader told BBC1's Andrew Marr Show.
"And I think that job is made more difficult if you have years and years of tying yourself up in knots having arcane debates about the precise terms of the membership of the European Union before we get to a referendum.
"It is not in the national interest when we have this fragile recovery, when we have a very open economy which is very dependent on investors in the car industry and the banking system and so on.
"You must always, when you are trying to piece together a recovery, foster those precarious conditions of greater confidence in the economy, you mustn't do anything to make that more difficult."
He claimed that "most businesses I speak to...are extremely concerned".