Only 12% of the public believe Michael Howard will be elected prime minister, with 78% believing he will never lead the country, a BBC Newsnight/ICM poll suggests.
22% of those polled said the Tories are the most effective opposition party
Even among Conservative supporters polled, the majority (65%) believe he will never be PM.
The poll also revealed that nearly twice as many people questioned believed the Liberal Democrats are a more effective opposition to the government than the Conservatives.
The findings amount to more bad news for the party and its leader, coming just days after the Conservative's humiliating defeat in the Hartlepool by-election.
The party finished fourth after netting fewer votes than the UK Independence Party.
Nearly a quarter (22%) of those polled believed the Conservatives were the most effective opposition party, compared with 42% believing the Liberal Democrats were.
On the war in Iraq, more than half of the sample (52%) believed Mr Howard's criticism of the way the government made its case for war was motivated by a desire to score political points over Tony Blair.
And 34% of those polled believe Mr Howard genuinely objects to how Tony Blair made the case for war.
Even amongst the Tory voters questioned, 38% believe Michael Howard was motivated by political point scoring.
The poll also asked voters about their attitudes to taxation and whether a tax-cutting message from the Tories would make them more likely to vote Conservative.
The poll found 20% said that if the party had "a firm and specific promise to cut taxes" it would make them more likely to vote Tory, with 21% saying they would be more likely to vote Conservative if they pledged "to cut taxes if and when the state of public finances allow."
According to the poll, 41% would be more likely to vote Conservative if they said it would "spend any spare money on public services and not reduce taxes".
The telephone poll of 1,004 people was conducted between 1 and 3 October.
Shadow Chancellor Oliver Letwin told the BBC's Newsnight programme no-one could "predict what will happen at the general election".
"There is a perfectly reasonable chance we can win it," he said.
But Mr Letwin added: "We never take the electorate for granted.
"Two years ago I said it would be a miracle if the Conservative Party was elected.
"That is how it looked then, I do not think that is how it looks now."
"But I know it is a tough fight because we live in a democracy, and a democracy means putting forward a programme conceived in the interests of the nation, honestly and straightforwardly, and then delivering on it if elected."
Voters were "really disillusioned" with the Labour government, Mr Letwin told BBC News.
"We have to get across the message there is a serious alternative... to get the state off people's backs, allow schools and hospitals to run themselves - so your school is run by a teacher who knows your child's name".
He also cited the need to "get police onto the streets, get crime under control by those means, get immigration under control and have a lower-tax economy."
A Conservative government would also "thin down" bureaucracy and let people "run their own affairs more", Mr Letwin added.