The leader of the Conservatives MEPs has accused the Government of "snarling like a pitbull across the Channel".

Speaking in the European Parliament's London office, Richard Ashworth warned: "We're raising the tempo so that expectations are becoming too great."

He also claimed the Tories were making themselves "pretty unattractive and difficult to work with" in the EU. The party's European leader went on to say many nations were on the UK's side, including Sweden, Finland and Denmark.

It came as Chancellor George Osborne raised the prospect that Britain could leave the European Union unless there is change in Brussels.

He told German newspaper Die Welt that although he very much wanted the UK to continue as an EU member state, for this there would have to be reforms.

"I very much hope Britain remains a member of the EU. But in order that we can remain in the European Union, the EU must change," he said in comments published yesterday, but made on Tuesday while visiting German Chancellor Angela Merkel in Berlin. His comments follow US assistant secretary for European affairs Philip Gordon's statement that President Barack Obama's administration wanted "a strong British voice" in the EU and referendums risked turning countries inward.

Mrs Merkel had warned any attempt at blackmailing member states into accepting change would backfire.

Bundestag European affairs committee chairman Gunther Krichbaum said a referendum could leave the UK isolated in Europe.

Conservative MP for South Northamptonshire Andrea Leadsom rejected Mr Ashworth's attack as unfounded, but foreign affairs spokesman in the House of Lords, Liberal Democrat Lord Wallace, conceded other EU member states were finding it "increasingly difficult to accept Britain's demands".

He said the UK was now suffering from the fact that "they read our press but we don't read theirs".

A Treasury aide insisted Mr Osborne's comments were fully consistent with the Government's position.