A new poll today put David Cameron's Conservatives 13 points ahead of Gordon Brown's Labour Party.
The ICM survey for the Sunday Telegraph follows a string of polls in which Labour reduced the Conservative advantage to single figures.
It will raise a question mark over claims that a "Brown bounce" in response to the PM's handling of the economic crisis has restored Labour's fortunes after a woeful summer in which Mr Cameron's lead stretched at times to more than 20 points.
In the wake of Thursday's by-election victory at Glenrothes, some Labour MPs were even urging the Prime Minister to call an early election.
However, today's poll underlines the dangers of going to the country next year, giving the Tories a comfortable lead on 43%, against 30% for Labour and 18% for the Liberal Democrats.
If repeated in a general election, the figures would give the Conservatives an 80-seat majority in the House of Commons, the Sunday Telegraph said.
In another boost for Mr Cameron, he was rated the British leader best-placed to build a new relationship with US president-elect Barack Obama, beating Mr Brown by 40% to 35%.
But Mr Brown and Chancellor Alistair Darling were rated most-trusted to steer Britain through the economic downturn.
:: ICM interviewed 1,005 adults by telephone on November 5 and 6.
Shadow foreign secretary William Hague denied that the "wind had turned" for Labour following their Glenrothes win.
He told Sky News' Sunday Live: "David Cameron and I and the rest of the shadow cabinet have always stressed, even when we were 20-odd per cent ahead in the opinion polls, that we must never be complacent about the next election.
"But I think Labour would be kidding themselves if they thought that the result at Glenrothes signalled some great change in the mood of the country.
"That's certainly not what I see out there, even with people I've talked to in the street this morning, and it's certainly not what's shown in a widening Conservative lead in the opinion polls today."
Mr Hague added: "People know that Gordon Brown left this country the worst prepared for recession of all the major economies."
Foreign Secretary David Miliband said that the Glenrothes result showed it was "game on" again in the fight for the next general election.
Mr Miliband was widely suspected of trying to position himself as a potential successor to Mr Brown during the summer, when he wrote a high-profile article about Labour's future without mentioning the Prime Minister.
The impression of a coup-in-waiting was heightened further at Labour's conference in Manchester in September, when the Foreign Secretary appeared to court media attention and was overheard talking about the need to avoid a "Heseltine moment" in his keynote speech.
But he today insisted that he had never supported the behind-the-scenes grumbling about the PM's performance and was convinced that Mr Brown was the right man to lead Labour into the next election.
"I have never supported the murmurings and rumblings in respect of triggering a leadership contest," Mr Miliband told BBC1's Andrew Marr Show.
"Gordon was the right man last year, he is the right man this year and he is the right man next year."
He added: "I think there is a sense of 'game on', because over the last three to four months we have seen a Government reacting decisively to the most important challenges of the international and domestic economy and we have seen an opposition falling apart in terms of its own prospectus.
"I think that is a signal and important moment in British politics, because it is saying that there is a real fight to be had out there about the future of the country. That is something I think we should relish."Reuse content