It comes after a Liberal Democrat Cabinet minister indicated David Cameron’s commitment to an in/out referendum would make a second coalition with the Tories “incredibly difficult” to agree.
The Lib Dem leader, launching his party’s election campaign, said it was “stating the flaming obvious” that the UK needed to be at the heart of Europe.
He said large parts of the Tory party were “straining at the leash” to leave the EU, potentially putting the economic recovery at risk.
Speaking yesterday in Abingdon, part of a key marginal seat the Lib Dems are hoping to win back from the Conservatives, Mr Clegg also hit out at Labour, saying he was “dismayed” by Ed Miliband’s failure to spell out details of when he would balance the nation’s books.
Energy secretary Ed Davey, tipped as a potential successor to Mr Clegg if he is forced out after the election, said the issue of Europe could be a stumbling block in any fresh coalition negotiations with the Tories.
He said that the Tory policy on Europe amounted to “economic and environmental irresponsibility of the highest order” and any deal that involved supporting an in/out referendum would be “incredibly difficult” to envisage.
Speaking in the Oxford West and Abingdon seat, won by the Tories with a majority of just 176 in 2010, Mr Clegg said: “Of course we have different views to the Conservatives. I’m the leader of the Liberal Democrats, David Cameron is the leader of the Conservatives.
“They have a completely different attitude towards Europe. They have this hokey cokey where one day they want to leave, the next day they don’t want to leave.
“We are unambiguous as a party that says ‘yes, Europe needs to be reformed, yes there needs to be a referendum when a decision needs to be made about the transfer of powers to the European Union, we guaranteed that in law’.”
He added: “Of course it would be an economic act of self-harm to leave the European Union.
“Large parts of the Conservative Party and Ukip appear to want Britain to cut itself off from what is the world’s largest marketplace with hundreds of millions of customers for British goods and services.”
He added it would be a “terrible thing” for the British economy.
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