The results of which could play a pivotal role in Boris Johnson's political future could be determined by the close of the two crucial byelections in Wakefield and in Honiton.
If the Liberal Democrats overturn a 24,000-plus majority in Tiverton and Honiton, the prime minister could be challenged by disgruntled Conservative MPs.
The Devon seat, which has been held in various incarnations for more than a century, was represented by Neil Parish from 2010 onwards. Parish resigned after admitting he had watched pornography in the Commons.
Wakefield is expected to declare first on Friday, given the West Yorkshire constituency is more geographically concentrated.
The vote took place after the sitting Tory MP resigned in disgrace. Imran Ahmad Khan stepped down after being convicted of sexually assaulting a teenage boy.
While Labour is widely predicted to win in Wakefield, a constituency that consistently held up to the 2019 election, a Tory defeat in Tiverton and Honiton would send significant jitters through the parliamentary Conservative party.
If the Lib Dems win, it's believed that this would be the largest numerical majority overturned in a byelection, although there have been bigger percentage swings in other seats.
Both the Lib Dems and Tories have described the Devon race as too close to call. The Lib Dems efforts on Wednesday hand-delivered more than 40,000 leaflets, which could tip the result in their favor, could be tipped by the sheer scale of the Lib Dems efforts on the ground.
Johnson is in Rwanda for the Commonwealth heads of government summit before moving to the G 7 and Nato summits in Germany and Spain, keeping him out of the country for the next week.
If there is a notably significant swing back to Labour in Wakefield, Tory backbenchers may try to oust Johnson in his absence.
After this month's no-confidence vote, 41% of Tory MPs voted against him, under party rules he is safe from a similar challenge for a year. These rules can be changed.
The pressure on Johnson will be particularly intense if the Wakefield result indicates that Labour under Keir Starmer is making significant inroads into red wall seats, adding to the pressure from the resurgent Liberal Democrats.
In December, the Lib Dems took a rural, Britons-minded Tory stronghold and overturned a majority of nearly 23,000 to win the North Shropshire byelection, after former incumbent Owen Paterson quit over a lobbying scandal.
Hundreds of similar blue wall seats could fall due to widespread dislike of Johnson among more liberal-minded Conservative voters after a win for the Lib Dems in Chesham and Amersham last June, a commuter-belt constituency north-west of London.
The initial confidence vote, coupled with the fact that Johnson is no longer an electoral asset, could see Tory MPs turn against the prime minister, although a new challenge is viewed as unlikely before autumn.