David Cameron has met Conservative backbenchers amid the fallout from his veto of an EU treaty change aimed at tackling the eurozone crisis.About 30 MPs, said to be from all sides of the party, visited his official country residence on Friday night.One Eurosceptic MP - Andrew Rosindell - said the PM had been "very relaxed" and the mood "extremely positive".Mr Cameron's decision is facing intense scrutiny, with some Lib Dem critics saying he is appeasing the Tory right.His Deputy Prime Minister and the Lib Dem leader, Nick Clegg, has also warned that any Eurosceptics "rubbing their hands in glee" about the outcome of the EU summit should "be careful what they wish for".He said there was "clearly an increased risk of a two-speed Europe in which Britain's position becomes more marginalised, and in the long run that would be bad for growth and jobs in this county".Critics from within the UK and across Europe have warned that the prime minister's decision to block the proposed EU-wide treaty change will leave the UK isolated.Labour said the UK would be left out of key European Union decisions affecting the country's future.It now looks likely that all 26 other members of the European Union will instead agree to a new "accord" setting out tougher budget rules.Defending his decision on Friday, Mr Cameron said the UK remained a "full and very influential member" of Europe on the issues that mattered to it."Membership is in our interests and I've always said if that's the case I'll support our membership," he said."Membership of the European Union is good for us."German Chancellor Angela Merkel said she "regretted" that the UK was "not able to go along the same path" as the rest of Europe.French President Nicolas Sarkozy said Mr Cameron's insistence on a protocol allowing London to opt out of proposed changes to the rules governing financial services was "unacceptable", because a lack of regulation was behind much of the debt crisis.Meanwhile, the top US military commander, Gen Martin Dempsey, says he is concerned about "the potential for civil unrest" as the financial crisis in the eurozone continues.Mr Cameron said the abandoned treaty change involving all 27 members had been in danger of "distorting the single market"."I think I did the right thing for Britain," he said. "We were offered a treaty that didn't have proper safeguards for Britain and I decided it was not right to sign that treaty."He said the UK was a leading European player in Nato and an important member of the single market - but was not in the eurozone or the Schengen agreement on open borders.But Labour leader Ed Miliband said the prime minister had "mishandled these negotiations spectacularly"."It's a terrible outcome for Britain because we are going to be now excluded from key economic decisions that will affect our country in the future," he said."What I find incredible is that he simply ended the negotiations yesterday and said that was it. He could have carried on negotiating today to get a better outcome for Britain."UK Independence Party leader Nigel Farage said the outcome was "the worst of all worlds" for the UK, leaving the country in Europe but without power.Labour and UKIP both warned that Mr Cameron had actually secured no new safeguards for the City of London - despite stating that that was a priority.