Pollster Sir John Curtice has warned that Sir Keir Starmer is as unpopular as Labour leaders before him who went on to lose general elections.
Despite holding an almost 20 point lead in the polls, Curtice said Starmer is failing to capitalise on the Conservative Party's unpopularity.
He explained: "We've got two unpopular leaders.
"I went to a presentation of young researchers working in the polling industry.
Pollster Sir John Curtice has warned that Sir Keir Starmer is as unpopular as Labour leaders before him who went on to lose the election
PA
"And the guy hosted this lovely presentation, in which they basically said: 'You know what, if you take past precedent, the Government is heading for defeat. But so, also, is the Opposition.'"
Speaking to the Express, he added: "And part of that was basically Starmer looks like an unpopular Leader of the Opposition, like previous leaders of the opposition who have never made it.
"But equally Sunak is an unpopular Prime Minister, like previous prime ministers who have been turfed out by the electorate.
"And neither party frankly has a leader that is a particular positive, at least so far as public perceptions of this are concerned."
The polling professor at the University of Strathclyde warned Sunak has even deeper problems, noting that the PM is now as unpopular as the Conservative Party itself.
Curtice also warned the PM against taking personal swipes at Starmer - as the Tory Party gears up to criticise the Labour leader's time as the Director of Public Prosecutions.
He explained: "We’re now being told that they are going to engage in personal attacks against Starmer. Well, if Keir Starmer was a really popular politician, it might be worthwhile, but he isn’t.
"Apart from the fact that he's not Jeremy Corbyn, he's not attracting people to the Labour Party."
The pollster added: "When Sunak became Prime Minister, he was less unpopular than his party, although he wasn't as popular as he had been before the revelations about his wife's non-dom status.
LATEST DEVELOPMENTS:
"But now basically, if you follow YouGov’s data and everybody else's data showing the same thing, he’s become less popular during the course of this year.
"According to YouGov, he's now as unpopular as his party.
"So basically, in a sense, the crucial attribute that Sunak was meant to be able to deliver for his party, which is a modicum of popularity, that's gone."