Nick Clegg says Cameron's EU goal 'wholly implausible'
Nick Clegg has said the UK risks "tying itself in knots" and neglecting more important issues by trying to renegotiate its EU membership.
The Lib Dem leader said it was "wholly implausible" to think the rules could be rewritten to "benefit us and disadvantage everybody else" .
He said the aims of David Cameron's proposed renegotiation were "vague" and uncertainty could hit growth and jobs.
The prime minister has insisted the UK "is not turning its back on Europe".
Speaking at the World Economic Forum in Davos, Mr Cameron said the EU was losing out to other growing economies and the union must be reformed so it was "an engine for growth, not a source of costs for business and complaints for our citizens".
"This is not about turning our backs on Europe - quite the opposite," he argued. "It is about how we make the case for case for a more competitive, open and flexible Europe and how we secure the UK's place within it."
The Conservative leader has promised to hold a referendum on whether the UK should stay in the EU, although the pledge would be dependent on him being prime minister after the next election, expected in 2015.
The move has been welcomed by most Conservative MPs but both Labour and the Lib Dems have said they do not support such an in/out referendum, arguing that uncertainty about Britain's future would undermine the UK's economic prospects.
Speaking on his weekly phone-in on LBC radio, Mr Clegg said Mr Cameron was "entitled" to set out what he would do in a future Conservative government and made clear he had been given advance notice of the PM's referendum commitment.
He said he did "not fear" the principle of a referendum and that his party had supported legislation guaranteeing that the public would be consulted before any further powers were transferred to Brussels.
But he said he disagreed with the timing of Mr Cameron's announcement, which he said was a distraction from more urgent issues, and which he believed had more to do with the prime minister's "own political purposes" than the country's wider interest.
"Where David Cameron and I part company is I simply don't understand the point of spending years and years tying yourself up in knots first renegotiating the terms of Britain's membership in ways that at the moment are completely vague.
"I think that discourages investment and inhibits jobs and growth which has to remain our absolute priority."
There were two likely outcomes from the process that Mr Cameron had set in train, he suggested.
"Either it is basically a bit symbolic - so you tweak the working time directive and a social law here or an environmental law there that everybody will agree with so, in which case, what is the fuss all about?
"Or you are going to do something which I think is wholly implausible which is basically totally rewrite the rules to benefit us and disadvantage everybody else which is clearly not going to be agreed to."
Although Mr Cameron talked about returning powers from Brussels to national governments in areas such as the environment and social affairs, he has yet to give specific details.
Mayor of London Boris Johnson said he would be prepared to campaign for EU withdrawal if he did not believe the deal Britain was getting was acceptable.
While he personally preferred to remain in the EU and he believed negotiations would be successful, he added. "You cannot go into any serious negotiation of this kind without at least being able to walk away."
Labour has warned the prospect of a protracted renegotiation followed by a referendum could send out the wrong signal to business.
"We have traditionally said 'come to Britain because it is a favourable climate and you will have access to his huge market'," said former Labour Europe minister Peter Hain. "Now we are on a road which could lead us out of Europe and out of that market and that is a decision which is going to affect investment."
While expressing concern about countries "cherry picking" parts of the EU they wanted to adhere to, EU leaders have been emphasising their wish for the UK to remain within the organisation.
The Irish prime minister Enda Kenny suggested Britain could secure many of the changes it wanted "from inside" the EU while Dutch counterpart Mark Rutte said it was "vital" for both parties that the UK remained a member.
"The UK outside the EU would be an island somewhere in the middle of the Atlantic Ocean between the US and Europe," he said. "It would not be connected with any of those two."
And Italian premier Mario Monti said he believed the British people would choose to remain within the union when presented with such a "clear-cut question".
Downing Street said Mr Cameron had spoken to Mr Kenny, Mr Rutte and Mr Monti whilst attending the World Economic Forum and also met German Chancellor Angela Merkel on the margins of the conference.
He is due to meet Prime Minister Fredrik Reinfeldt of Sweden and Prime Minister Jens Stoltenberg of Norway later.