LABOUR will need to match the scale of the SNP’s last win in Rutherglen and Hamilton West if the party are to meet their expectations for the General Election in Scotland, according to a leading pollster.

Professor Sir John Curtice said the seat is a “must-win” for Sir Keir Starmer as it was a relatively marginal SNP-held seat and previously won by Labour under Jeremy Corbyn’s leadership.

He said if Labour won the by-election taking place on Thursday, how well they win will be just as important.

Visiting the constituency on Friday, Starmer said it would be a “milestone” on his party’s “hard road” back to power.

Curtice, professor of politics at Strathclyde University, told the Sunday National: “I’d be inclined to say it would be a much bigger milestone if they fail to win.

“This is a relatively marginal SNP-held seat – it was won by Labour in 2017.

“Even if the by-election had been held six months ago it should have been a close contest, as by that stage even though support for the SNP was not particularly down, Labour’s vote was around 10 points up and that’s all Labour need to do in order to be able to pick the seat up.

The National: Labour leader Sir Keir Starmer at a party rally in Rutherglen ahead of the Rutherglen and Hamilton West by-election. Picture date: Friday September 29, 2023. PA Photo. See PA story POLITICS Rutherglen. Photo credit should read: Andy Buchanan/PA Wire

“Particularly as Labour won the seat under Corbyn just means that Starmer has to win it.”

He added: “What we are looking for in this by-election, assuming Labour win, is how well they win.

“They ought to win relatively comfortably if they are going to match the expectations generated by the Scotland-wide polls – of course, by-elections don’t necessarily exactly follow the national polls, but they want it to be in roughly the same place.

“That probably implies more or less being as far ahead in terms of the share of the vote as the SNP were in 2019. That would be a 10% swing with current national polls on average, although there is some variation pointing to about 11 points.

“If it starts getting much below that, then sure Labour would still expect to pick up some seats north of the Border – but not necessarily on the scale that some at least have been suggesting they are hoping for.”

Polling expert Mark Diffley, founder and director of the Diffley Partnership, pointed to the turnout figures as well as the margin of victory as a key aspect of the by-election.

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“The national polls tell us that Rutherglen is well within Labour’s reach given what we’re seeing in terms of national swing,” he said.

“Perhaps the thing to be looking out for is what the margin of victory will be and what then that tells us – given the turnout will probably be quite low in election terms, they usually are in by-elections.

“There may be some limitations to what we can say about what it tells us about the national picture next year for the General Election, but it will be a very significant barometer of what’s going to be ahead of us.”

He added: “Who won and by what margin and then turnout – what that says about the kind of bigger state of play will be particularly important.

“Across the country, one of the key stories that came out of 2017 – which, of course, was a bit of a bump in the road for the SNP from which they then recovered in 2019 – but it was the extent to which they got their vote out.”

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Recent weeks have seen politicians from all parties hit the campaign trail in Rutherglen and Hamilton West.

Diffley said the intensity and small areas involved in by-elections meant such campaigns could make a difference to the vote.

He also said the results from real voters will come at a crucial time for parties in the run-up to the General Election expected next year.

“Rutherglen itself may actually change the whole thing as well in either direction,” he said.

“Labour winning will be symbolically really, really important for them and not just in Scotland, but it will tell them about their chances UK-wide.

“But what if they win but only just – what do they do then?

“What if they win, but really, really, significantly and the SNP vote completely collapses? What do the SNP do?”

He added: “I suspect it’s far enough out from a General Election – even an early General Election won’t be for another six to nine months. Even if it’s June or May, that’s still long enough away for parties to sort of reframe their manifestos, their messages.

“As a kind of exercise and understanding where people are at, there’s nothing that beats a by-election.

“For all sorts of reasons, this by-election will be really important.”