Clarke is most popular Conservative among party members and public

Kenneth Clarke's hopes of winning the Tory leadership are given a huge boost today by an opinion poll showing he is the most popular of the five candidates in the contest.

The survey gives backing to Mr Clarke's claim that he is the candidate most likely to lead the Tories to victory at the next general election. He is more popular than his main rival Michael Portillo among both ordinary voters and Tory supporters.

The Mori poll for The Times shows that 32 per cent of voters believe that Mr Clarke would make the best job of leading the Tories, with 17 per cent naming Mr Portillo, 7 per cent opting for Iain Duncan Smith, 6 per cent Michael Ancram and 4 per cent David Davis.

Among Tory supporters, Mr Clarke enjoys a narrower lead. He is on 29 per cent to Mr Portillo's 25 per cent, with Mr Duncan Smith on 13 per cent, Mr Ancram on 12 per cent and Mr Davis on 5 per cent.

In the event of a run-off between them, Mr Clarke would win the backing of 51 per cent of the public and Mr Portillo 25 per cent. Among Tory supporters, Mr Clarke leads Mr Portillo by 49 per cent to 39 per cent.

The poll was taken before Mr Clarke entered the leadership race on Tuesday and will give him the momentum he needs after delaying his decision on whether to stand. Last night Mr Clarke said: "I have to treat these figures with caution, but they do seem to support my argument that I'm the best-placed to help the Conservatives win a general election."

The debate over the Tories' future intensified yesterday as Mr Ancram and Mr Portillo clashed over whether the party needs to make urgent and sweeping changes in the wake of its crushing general election defeat.

Mr Ancram, the former Tory chairman, insisted the Tories must not be "panicked" into change and said their first priority should be to end the disunity and "factionalism" which he said had undermined the party for a decade or more.

But Mr Ancram was dubbed the "Corporal Jones" candidate by MPs backing Mr Portillo, in a reference to the "don't panic" message of the character in the TV series Dad's Army. One Portillo ally said: "Mr Ancram appears to be saying we should suffer a third landslide before we do anything about it."

Francis Maude, the campaign manager for Mr Portillo, warned that the Tories could face 18 years in the political wilderness unless they embraced radical change.

He said: "It is easy for us active, committed Conservatives to believe that we will sooner or later benefit from the return swing of the electoral pendulum. We should make no such assumption. All the evidence is that the pendulum, if it still swings at all, does so rather slowly. So Labour found during the eighties and nineties."

Mr Ancram, unveiling his personal manifesto, sought to dispel his image as the "no change" candidate by promising, if he became leader, to set up a commission which would "think the unthinkable" on policy.

Mr Davis promised to shut down under-performing schools, while freeing successful ones from government interference and allowing them to expand at the cost of failing neighbouring schools.