Selby in Yorkshire, Somerton in the south west and Uxbridge in the London suburbs: from rural to town, from north to south – the three by-elections up this Thursday will tell a bigger story of the state of our politics, with records up for grabs.

In these three seats – and the prospect of at least two more additional by-elections to come in Mid Bedfordshire and Tamworth – there is so much trepidation for all of those politicians in play, but undoubtedly in the spotlight is the struggling prime minister, Rishi Sunak.

For a governing party, mid-term elections are never comfortable, but this particular set could cast the dye on his troubled premiership. Three by-elections in one day from a disparate set of battlegrounds and the Tories are bracing to lose all three.

That would make Mr Sunak a record breaker in unwelcome ways. He’d be first PM since Labour’s Harold Wilson in 1968 to lose three by-elections in a single day and he’d suffer the ignominy of being the PM that saw Labour overturn the biggest Tory majority in a by-election on record, should it flip a 20,137 majority to win Selby. A lot is at stake.

Read more: Everything you need to know about this week’s votes in Uxbridge, Selby and Somerton

Labour win in Selby would be ‘totemic’

Labour say Selby hangs in the balance, while one senior Tory – not trying to spin – tells me that while Conservative Campaign Headquarters thinks there’s a chance the Tories will hold on in Selby, they think the party will lose all three.

“We’re in the death throes and I can’t quite see a way forward and they are stuck managing defeat,” says one former cabinet minister. “[Sunak’s] an unlucky general. Every time he makes a announcement something else blows up, now they are working on the hope that they only have one term in opposition.”

But Selby is the Conservatives’ 249th most vulnerable seat. If Labour wins that, who’s to say they can’t gain the 124 seats they need for a Westminster majority?

Labour sources agree that losing Selby would be “totemic”, not just because Starmer would break a record, giving him even more momentum into a general election, but because of the psychology of what it does to Tory MPs.

Labour are touchy that the Conservatives have turned holding Selby into a victory given that the swing required to come even close to taking this seat in a general election – 17.9 per cent – is way beyond the swing Sir Keir needs to secure to win at the next general election.

“For Labour, I think expectation is that we will win Uxbridge and have to explain it if we don’t win,” says one senior Labour insider. “I think what is ludicrous is if people criticise us for not winning Selby. There are far too many Tory voters there, so if we take it will be big historically.

“But actually, it will be extraordinary if we run it close given the majority. The difference between losing by 10 and winning by 10 will be a big deal in terms of how the media cover it, but a strong second place puts us on track for winning it [with redrawn boundaries] at the general election.”

‘I think they are just running us into the ground’

Talk to Westminster insiders and the mood is that Somerton & Frome in the south west with a 19,000 Tory majority will go back to the Lib Dems. Uxbridge has been made more difficult to gauge due to the very live row about the Ultra Low Emission Zone air tariff being introduced by Labour mayor Sadiq Khan, which the Tories have grabbed to attack their opponents.

But when we visited Uxbridge this week, the overwhelming view from voters – even Conservative supporters – was for change.

Laura, an NHS nurse on maternity leave, told me that she didn’t believe the Conservatives could hold the seat.

“It can’t continue like this. I mean, it’s been a long time coming and I think they are just running us into the ground it seems.”

Anu, a Boris Johnson backer, and his partner Bijal, told me they were also considering going back to Labour having supported Mr Johnson in the past. “I think they’ve got quite a good chance,” Bijal told me. “We’re thinking, should we, should we flick the switch and go back to Labour?”

Meanwhile Mo, a hairdresser with her own salon just off the high street, was a Johnson backer, but now wants change as she struggles to keep her two-decade old business above water. “My shop was always full, but now we have to give more, people don’t know whether to spend their money.”

Both Labour and the Tories tell me that they are picking up “real anger’ on the doorstep in Selby. One senior Conservative told me canvassing was like a “bin fire” with traditionally Conservative voters telling them they were not going to turn out, while a Labour source says the Tories have nothing to offer core or swing voters on the doorstep.

“There’s a cost of living crisis, taxes are up, none of the five pledges are being hit,” says one senior figure. “In Uxbridge, ULEZ at least gives some reason for voters to mobilise.

“Outside of that, what do they have to offer after 14 years? Cost of living crisis, high inflation, high interest rates, chaos at the borders, a broken NHS, sewage in our rivers and then you ask voters to give you another chance?”

‘Warriors against complacency’

For Labour, Thursday is another stepping stone on Sir Keir’s path to power. Whether he takes one or two of these seats – not winning any is not an option – he will frame this as another staging post to a Labour government.

The question really for Labour is whether they can call this a Blairite win. Three of the top four swings for Labour occurred before Tony Blair became PM, in by-elections in 1994, 1996, 1997. If Labour do win Selby then it would be allow Starmer to claim his party is performing at a level not seen since the Blair era.

They are taking nothing for granted, with one senior Starmer adviser telling me this week that the Labour leader describes himself and the inner team as “warriors against complacency”.

The latest symbol of his discipline was the decision to maintain the two child limit for child benefit, which sparked consternation within the party. “We want to fix problems to Tory benefit system and address child poverty but the country can’t afford it,” explains one senior insider.

“We can’t spend money we don’t have and that means taking tough choices. It’s helpful to have this out there before the National Policy Forum, where people think we are 20 points ahead and we have this big lead and we can do all sorts of things and that is toxic thinking, that is what loses elections.”

Labour insiders keep talking to me about the mis-steps in the 1992 general election campaign, when then shadow chancellor John Smith’s mini-budget said the better off would pay for higher pensions and child benefits. The plan blew up, spectacularly, in his face, lending itself to the Tories’ slogan ‘Labour’s tax bombshell’ as John Major edged victory. There will be no re-run of that. “We are going to do nothing to lose focus or discipline.”

Losing Uxbridge would hurt the Tories, but with a majority of around 7,000, a defeat here is not worse than other defeats in this parliament. Selby is another matter. If it turns red, the psychological damage to Mr Sunak and his party will be immense.