Several European leaders have criticised British Prime Minister David Cameron's demand for radical reform of the EU and promise of an "in-out" referendum on UK membership.
"If Britain wants to leave Europe we will roll out the red carpet for you," said French Foreign Minister Laurent Fabius on Wednesday.
Demanding changes in the rules was as if Britain had joined a football club and then suddenly said "let's play rugby", Fabius added.
German Foreign Minister Guido Westerwelle said Britain could not treat Europe like an "a la carte" menu from which it could pick and choose policies it liked.
"Cherry-picking is not an option," he said.
Cameron had promised to give the British people a straight referendum choice on whether to stay in the EU or leave, provided he wins an election in 2015.
"It is time for the British people to have their say. It is time for us to settle this question about Britain and Europe," the prime minister said.
"When we have negotiated that new settlement, we will give the British people a referendum with a very simple in or out choice to stay in the EU on these new terms; or come out altogether," the Tory leader added. "It will be an in-out referendum."
Cameron ended months of speculation by announcing in a speech the plan for a vote sometime between 2015 and 2018, shrugging off warnings that this could imperil Britain's diplomatic and economic prospects and alienate its allies.
Martin Schulz, the head of the European Parliament which with the European Commission was the main cause of Cameron's criticism of "sclerotic" EU decision-making, reacted angrily to his comments.
Britain was pointing the finger but was "overwhelmingly to blame for all the delays in Europe", said Schulz. "He just wants change in the single interest of Britain and that's not fair."
In Germany, where Angela Merkel's conservative sympathies for Cameron's party are overshadowed by anger at their exit from the centre-right EU bloc and his veto of her fiscal pact, the view is that the UK leader has painted himself into a corner.
Carl Bildt, the Swedish foreign minister, said the idea of flexible membership floated by Cameron "sounds fine" but would
lead to there being "no Europe at all. Just a mess."
Cameron's Conservative Party would campaign for the 2015 election promising to renegotiate Britain's EU membership.
The response to Cameron's long-awaited speech was not uniformly negative, however. Among sympathisers was Czech Prime Minister Petr Necas, whose government was the only one other than Britain's not to sign the fiscal pact. He said he shared Cameron's wish for a "more flexible, more open" EU.
The prime minister said he would prefer Britain, the world's sixth biggest economy, to remain inside the 27-nation EU, but he also made it clear he believes the EU must be radically reformed.
A new EU must be built upon five principles, he said: competitiveness, flexibility, power flowing back to - not just away from - member states, democratic accountability and fairness.
Al Jazeera’s Laurence Lee, reporting from London, said: "What he [Cameron] has done in this speech is give the European Union a deadline, almost as if he's holding it hostage, and saying if you don't change in these terms, then we will have a referendum and the British people will decide if we stay in or not."
The eurozone debt crisis is a main reason why Britain must reassess its relationship with the wider EU, Cameron said, adding that ever closer union was not Britain's objective.
He said Britain did not want to pull up the drawbridge and retreat from the world, but that public disillusionment with the EU was at "an all-time high".