Liz Truss has extended her lead over Rishi Sunak in the Tory leadership race, according to a poll of party members by YouGov.
The new survey put Ms Truss, the Foreign Secretary, on 60 percent of the vote and Mr Sunak, the former chancellor, on 26 percent.
That lead of 34 percentage points among decided Tory members is bigger than the previous YouGov poll last month, which put Ms Truss 18 points ahead. But doubts remain about the reliability of Tory membership polling. Far fewer such polls are carried out than general voter polling before elections.
Sir John Curtice, a leading polling expert, said that Mr Truss is likely to hold a “narrower” lead than thought after one survey put her only five points ahead of Mr Sunak.
Writing for The Telegraph, he cautioned against reading too much into the limited number of studies into the attitudes of Conservative Party members that have been carried out.
His remarks came as other experts warned that polls of party members are generally less accurate, and those who are not online may not be being reached at all.
“Liz Truss has near-universally been accorded the status of front-runner in the Tory leadership contest,” wrote Sir John. “We are repeatedly told that ‘polls’ put her well ahead. But there are now signs that her lead dela may be narrower than previously thought.”
A survey published on Tuesday by Techne, an Italian firm, surprised Westminster by putting Ms Truss on 48 per cent and Mr Sunak on 43 per cent.
The results indicated a huge shift from a YouGov poll a fortnight ago, which had the Foreign Secretary with a seemingly unassailable 24-point lead.
The poll of 730 Tory members found Ms Truss’s 24-point lead excluded those who said they did not know or said they would not vote. If they were included, 49 per cent of party members intend to vote for her, while 31 per cent intend to back Mr Sunak.
“In truth, there were already some straws in the wind… that perhaps Ms Truss’s lead was now proving rather narrower than in YouGov’s original finding,” said Sir John. “Apart from this still limited evidence, all of the polling of the Tory race has been of voters rather than of the members who actually have a vote.”
Experts have warned information that polling Conservative members is difficult and the lack of about them means there is a greater risk of inaccurate results.
Chris Curtis, the head of political polling at Opinium, said surveys of the party faithful are time-consuming and costly to carry out because firms typically need to canvass more than 100,000 of the general public to find enough Tory members for a viable sample size.
Even then, it is almost impossible for them to know how representative those people are of the overall party membership given the scant details available about them.
“When we’re doing surveys of the population as a whole, I know exactly how many over-65s there are, for instance, because the census tells us that,” he said. “The Conservative Party doesn’t tell us that about its membership. We can’t therefore weight the polls to be demographically representative.
“We are probably struggling to reach the Conservative Party members who are in their 80s and their 90s and who don’t use the internet.”
Mr Sunak has pointed to the polls to play up his underdog status, while allies of Ms Truss have said they are “paying no attention” to them.