UK voters are picking candidates to replace two MPs – one who was left mired in scandal and one who has become symbolic for the apparent fall of the ruling Conservatives.
Disgraced former whip Chris Pincher resigned as an MP for Tamworth after losing his appeal against a suspension for drunken behaviour.
Nadine Dorries was a loyal ally of ousted Prime Minister Boris Johnson. She announced she would quit her Mid Bedfordshire seat at about the time he decided he was leaving the House of Commons.
In a blistering attack on Prime Minister Rishi Sunak in her resignation letter, she said Conservative MPs would face an “electoral tsunami” at the next general election because of a “zombie Parliament where nothing meaningful has happened”.
She announced she was resigning but took weeks to complete the formal steps, in turn, delaying the by-election to Thursday.
At the last election, the staunch Brexit supporter won with a 24,664 majority in a seat that has been a Tory stronghold since 1931.
Conservative sources say they have research which shows its vote share could fall from the 60 per cent Ms Dorries won last time to 30 per cent for their candidate.
The deeply true-blue stronghold could still be won, with Labour on course for 22 per cent and Lib Dems on 12 per cent.
At the same time, the Conservatives – who are lagging Labour in national opinion polls – may wish to publicly play down their chances, so that any success is deemed better than expected.
If the Conservatives lose the seat, it would represent one of the biggest collapses of support in English by-election history.
The vote is being held on the same day as the Tamworth by-election, where the Conservatives also have a large majority of 19,634.
Labour is hoping to flip the majorities in both constituencies but has been cautious not to appear complacent, with a spokesman saying it is a “moon shot” to win either or both seats.
The votes will also be a crucial test for Mr Sunak's pitch that the Conservatives – after 13 years in power – represent a vote for change.
Mr Pincher, who has represented the Staffordshire seat since 2010, stood down after being found to have drunkenly groped two men.
The controversy remains one of the pivotal moments in Boris Johnson's downfall.
Mr Sunak's party – battered by the cost of living crisis, the fallout from a series of political controversies in Mr Johnson’s time, and the short-lived Liz Truss administration – is trailing in opinion polls behind Keir Starmer's Labour Party.
Recent surveys have shown Labour's poll lead narrowing after Mr Sunak announced a number of populist policies.
Labour is hoping Thursday's result will mirror the result of the northern Selby and Ainsty local election in July, where the opposition overturned a 20,000 majority.
Voters on the same day, however, narrowly backed the Tories in Mr Johnson's former Uxbridge and South Ruislip constituency in a local poll dominated by a plan to extend a scheme taxing the use of the most polluting vehicles in London
Mr Johnson won a landslide general election victory in 2019 with an 80-seat majority in parliament.
That win was partly due to “red wall” voters, former Labour supporters who backed the Conservatives for the first time.
The seats being decided on Thursday are traditional Tory voters, not new voters from Labour’s heartland.