A series of senior shadow cabinet ministers will be posted to Selby from this weekend as Labor makes a desperate effort to secure what would be a historic by-election victory for the party.

Wes Streeting, Yvette Cooper and Lisa Nandy, among the most recognizable names in the Labor Party, are scheduled to visit the North Yorkshire headquarters in the next 48 hours as the party seeks an unlikely victory. Securing the seat after Thursday’s vote would set a new record for Labor by overturning the Conservative majority, which stood at more than 20,000 in the last general election.

While it could be history making time for Keir Starmer, next week will be a more critical turning point for Rishi Sunak. The prime minister is not only facing three by-elections, all of which could be lost. He also awaits Wednesday’s release of new inflation figures that have become very important to his term. He has put reducing inflation above all other priorities and has vowed to cut it in half by the end of the year.

Three by-election losses would also risk prompting more Conservatives to declare they will resign in the next election. More than 40 deputies have already done so. Ben Wallace, the Secretary of Defense, is the last to announce that he is retiring.

Labor has poured resources into the Selby and Ainsty seat, which was left vacant by the resignation of Boris Johnson ally Nigel Adams. Meanwhile, there has been frustration among local Tory activists, who have complained about the absence of the party’s heavy hitters.

In a sign of a lack of trust in the Tory brand, local brochures barely mention the Conservative party, or even feature the color blue. Some Tories regard them as a “quasi-Green party” in appearance. They are also presented in a local newspaper format, one called the “North Yorkshire Chronicle” and another the “North Yorkshire Special”. Sunak, seen as an electoral asset in the seat, features heavily, along with candidate Claire Holmes.

The job requires a swing of 18.5% to win. The conservative majority in the last elections was 20,137. The current party record for unseating a Tory majority in a by-election is about 15,000, set in Mid Staffordshire in 1990. That contest was dominated by Margaret Thatcher’s plans to impose the poll tax.

While losing Selby would be grim for Sunak as the summer recess approaches, some Conservative MPs believe they could still disrupt Labor celebrations by defending the Uxbridge and South Ruislip seat vacated by Johnson. While Labor only needs to overturn a majority of 7,000, the Conservatives have had some success focusing the race on London Mayor Sadiq Khan’s ultra-low emission zone, which affects traffic in the area. “It’s harder than people seem to think,” said a Labor official.

Sunak is also facing a third assault from the Liberal Democrats on the south-west headquarters of Somerton and Frome. It was left vacant when Tory MP David Warburton resigned after admitting he had taken cocaine and drunk “incredibly potent” Japanese whisky. He was also accused of sexual harassment, which he denied.

Lib Dem polling data suggests the party trails narrowly with a crucial few days of the campaign remaining. At the end of last week, pundits said the data put the party at 39.5% and the Conservatives at 42%. The campaigners say the biggest remaining challenge is convincing Labor and Green voters to back them in defeating the Tories.

However, officials are optimistic of a victory, and internal discussions are now taking place over whether the Liberal Democrats should reconsider their ambitions in the South West, where they were strong before the coalition government in 2010.

An internal note from the party’s field campaigns manager, Dave McCobb, states: “The ease with which people have switched to us at Somerton and Frome, combined with the strong victory at Tiverton and Honiton last year, and our record performance in May 2022 and the 2023 local elections have convinced me that there is scope to expand our ambitions in our former heartland in the south-west.”

A Lib Dem source said: “If we can win a safe seat like Somerton and Frome, Conservative MPs in nearby seats sitting in much smaller majorities would cringe. A Lib Dem resurgence in the west of the country would be bad news for Rishi Sunak and good news for all those who want to get rid of this conservative government.”