John Curtice, professor of politics at Strathclyde University and Britain’s top polling expert, says Rishi Sunak has only a 5 per cent chance of winning the Tory leadership contest and that he would be “extraordinarily surprised” if Liz Truss does not take over from Boris Johnson as prime minister.

Curtice, who has been used by the BBC for decades as a polling guru during general elections, has a track record of making responsible – and accurate – predictions.

Curtice’s assessment is based on a YouGov poll for Sky News which showed that Truss had retained a 32-point lead over Rishi, matching a separate poll of Tory members by the ConservativeHome website.

Curtice said that YouGov and ConservativeHome have a “pretty good record”, adding: “Unless there is something that’s gone seriously astray this time it is difficult to believe that Sunak is going to make it.”

He did not rule out Truss’s share of the vote falling below 60 per cent, saying that the former chancellor could gain more support among undecided members.

“But below 50 it would count as a much bigger error in the polling than we’ve seen previously in the 2015 general election,” he said. “There’s a 5 per cent chance that Sunak could win it. Something would have to happen. Truss would have to foul up in some spectacular fashion. Even then it might be too late. The evidence in front of one’s eyes all points you in the same direction.”

The YouGov poll found that 66 per cent of members back Truss and 34 per cent back Rishi, excluding those who are undecided.

The race has tightened only slightly since a poll by The Times and YouGov a fortnight ago, when Truss had a 38 per cent lead. It suggests that Rishi’s blitz of television interviews and increasingly strident approach to the contest, particularly over Truss’s approach to the cost of living, are failing to have an impact.

Fifty-seven per cent of Conservative members say that they have already voted and another 38 per cent intend to do so. Truss retains a 37-point lead among those who have voted and a 15-point lead over Rishi among those yet to vote, with a significant proportion still undecided.

Rishi’s team have questioned the accuracy of the polls and said their on the ground evidence indicates a more optimistic scenario for their candidate.

Curtice said that while Rishi may have come across as more polished and articulate, Truss had been the better politician during the contest.

“If you’re trying to answer the question, ‘Which of the two candidates an Oxford tutor would mark the most highly?’ you would say Sunak,” Curtice said. “On the other hand if you were asking who was the better politician you would have to say Liz Truss.

“She has a very clear narrative which clearly resonates with her audience, she sticks to her guns, she doesn’t change her mind. She is still as much in favour of tax cuts as she was six weeks ago, she is Johnsonian in her style. The fascinating question is how well it will all survive once she’s got the job.”

Tory members harbour clear doubts about the ability of whoever enters No 10 to win the next general election. Four in 10 Tory members believe there will be a hung parliament or a Labour majority if Truss becomes prime minister, but the figures are even worse for Rishi.

There is apparent concern about Truss’s economic policy. She has said that she will cut taxes to “go for growth”, but 63 per cent of members said the priority should be getting inflation under control. Only 33 per cent said tax cuts should come first.

Ironically, this is the very line that Rishi has been taking but as far as some Tory party members are concerned, she is right even when senior Conservative leaders, among them William Hague, Michael Howard and Nigel Lawson, tell them she is wrong.

The Daily Mail and the Daily Telegraph, who have been campaigning for the foreign secretary, have put a spin on this by applauding Truss for challenging “treasury orthodoxy”.

Those who know about British politics suggest cynically that Truss is “pragmatic”, and that once she achieves her long held ambition of entering 10, Downing Street, she will say “circumstances have changed” and adopt many of the policies currently being advocated by Rishi.

There is speculation about her possible cabinet appointments, whether she will offer Rishi a job, what that might be (health secretary?), and whether he would accept.

The Times, among papers to carry the latest polls, published some intriguing letters from its readers.

One summed up: “The wise would pick Sunak, the ignorant would pick Truss. Says it all really.”