The landslide victory for Andy Burnham in Makerfield is unlikely to be repeated in a general election, according to the pollster Sir John Curtice.

He told GB News “Do you think the extent to which Burnham outpolled his party, which was probably of the order of about 15 points? No, I don’t think we could expect that to be replicated nationally. There are so many local factors operating to his advantage.

“One is, of course, the fact that he’s the Mayor of Manchester, a very popular Mayor of Manchester, has long out-polled his party in that respect. Two, the fact that he had quite good local connections with the constituency, he lives not far away and previously represented a next-door constituency.

“And three, of course, he was able to stand as both the representative of the Labour Party, but also the challenger to the Labour Party, he was the person whom, if you would vote Labour anyway, you voted for, but if you wanted to get rid of Keir Starmer, you voted for. And it’s pretty clear that quite a lot of people who might otherwise have voted Conservative, Liberal Democrats, or Green, and both those parties saw their support virtually disappear at Makerfield, they also switched in behind Andy Burnham.

“So, yes, Andy Burnham’s polling indicates he’s got quite popular, certainly far more popular than Keir Starmer. Most people would say he’s a better communicator than Keir Starmer, though that’s not very difficult. So certainly potentially presents a more formidable challenge to Reform at the national level, but I don’t think they expect Andy Burnham to pull off the kind of personal boost that he managed to achieve in the by-election.”

Asked if Burnham as leader would improve Labour’s prospects of winning a general election, Sir John said: “Probably, but not enough, is the answer to your question. These things are very, very difficult to judge, but we did have three exercises before the Makerfield by-election, asking people, well, how would you vote if Andy Burnham were Prime Minister?

“So you’re asking people to anticipate their reaction, they between them suggested that the boost to Labour might be between 3 and 7 points, and that therefore, at best, might put Labour very narrowly ahead of Reform.

“At this point, we have to remember two things: one, that 410 Labour MPs who hope to maintain their parliamentary careers, a one point lead over Reform, even if that would transpire, would still ensure that many of those MPs lost their seats and, by the way, would ensure that Reform is in a far better situation. That’s why Mr Farage is calling for a general election.

“The second thing to bear in mind is this: we are not yet halfway through the parliament, effectively. Therefore, in going to the country now, what Andy Burnham will be doing is trading the certainty of being able to have three years in office in return for the possible gain of gaining another two. Holding a general election early before the midterm of a parliament does not make much sense, unless you’re absolutely sure you’re going to win.

“Theresa May, of course, thought she was absolutely sure to win back in 2017 and it didn’t fall out in the way that she anticipated, even though she was in a far, far better position in the opinion polls than Andy Burnham is likely to find himself when he becomes Prime Minister.”