LONDON (Reuters) - Conservatives have overtaken the Labour opposition in an opinion poll for the first time this year, enjoying a bounce from Prime Minister David Cameron's veto of a new European Union treaty, the latest Reuters/Ipsos MORI poll showed on Wednesday.
The rise in support for Cameron's Conservatives is all the more remarkable given Britons' increasing pessimism on the economy, with only 12 percent expecting it to improve in the next year, the lowest figure since the credit crunch began to bite in September 2008.
Support for the Conservatives rose by seven percentage points to 41 percent, while backing for centre-left Labour slipped two points to 39 percent.
A YouGov poll for the Sun newspaper also put the Conservatives two points ahead of Labour, while the two largest parties were tied on 38 percent according to a survey by ComRes for the Independent newspaper.
The polls could worry Labour leader Ed Miliband, whose party is defending a parliamentary seat in a by-election in a West London suburban constituency on Thursday.
A national election is not due until 2015 and the Conservative-led coalition has vowed to serve until then to try to break the back of a big budget deficit.
Analysts say they expect the bounce to be short-lived as rising unemployment and public spending cuts are likely to cap Conservative support.
However, continued buoyancy in the polls may tempt some Conservative lawmakers to press for an early election to try to secure an outright majority.
The Liberal Democrats, the junior partner in the coalition that took power in May 2010, were on 11 percent in the Ipsos MORI poll, down one point, at less than half what they polled in the election 18 months ago.
Ipsos MORI spoke to around 1,000 Britons on December 10-12, after Cameron's historic use of his veto last week prevented the bloc from creating a new EU treaty to tackle the euro zone crisis. Cameron says he used his veto after failing to achieve safeguards he wanted for Britain's financial services industry.
The Liberal Democrats, who disagree with his decision, failed to support the Conservatives in a motion in parliament on Tuesday night commending Cameron's action.
The motion passed by 278 to 200, but all 57 Lib Dem MPs abstained, breaking coalition unity. The motion was put forward by Northern Ireland's Democratic Unionist Party.
The Ipsos MORI poll showed that support for Cameron's and finance minister George Osborne's response to the euro zone crisis had risen by four percentage points since November.
Fifty-six percent of those asked said the two had responded very or fairly well to the crisis, while only 40 percent said politicians such as French President Nicolas Sarkozy and German Chancellor Angela Merkel had responded well.
The EU summit fallout has reversed the effect of Osborne's autumn statement last month, when he cut economic growth forecasts and announced that austerity measures would continue until 2017, two years after the next election.
Commentators said they expected the Conservative bounce to be fairly short-lived.
"The surprise for me would be if it lasted longer than two months," said Justin Fisher, politics professor at Britain's Brunel University. "Cameron has been very good at selling his veto as something that is good for Britain," he added.
Economic factors are likely to dominate after Christmas.
"I don't think that David Cameron or George Osborne can sustain their previous popularity ratings," said Simon Lee of Hull University in northern England. "At some point, public patience with austerity is going to diminish."
Lib Dem leader Nick Clegg criticised the outcome of the EU summit as "bad for Britain," but many Britons are sceptical about the benefits of closer European integration and much of the press is openly hostile to the EU.
The slump in support for the Lib Dems means they have to remain in the coalition or risk an election drubbing.
Seventy percent of those polled identified the weak state of other countries' economies as the greatest threat to Britain's national interests.
Osborne has said that a recession in the euro zone would be likely to push the British economy into recession too. Britain does around half of its trade with the EU.
Sixty percent of Britons said the economy would get worse next year, against 12 percent who saw an improvement. Unemployment is expected to rise over the next year and the economy to grow slowly, at best.
Britons were divided on whether the government had made the right decisions on cutting the budget deficit. Forty-six percent said it had made the wrong decisions, while 44 percent backed tough cuts in public spending.
* Ipsos MORI interviewed 1,001 adults across Britain between December 10 and 12 by telephone; data are weighted to the profile of the population.
Editing by Alistair Lyon