The Greater Manchester constituency has been represented continuously by Labour for more than 90 years but sources from different wings of the party fear that the by-election could be won by either Reform UK or the Greens.
The rapid timetable is designed to constrict the amount of time the two parties have to build a campaigning infrastructure in the constituency.
While the decision by the prime minister and other officers from Labour’s ruling national executive to block Andy Burnham, the mayor of Greater Manchester, from becoming the candidate for the seat has been criticised by some MPs, the backlash has not been as great as some allies of Sir Keir feared.
However, several MPs – including MPs who supported the decision to exclude Burnham – said they now believed that if Labour lost the by-election it would trigger a destabilising burst of leadership speculation surrounding the prime minister because he is so closely associated with the decision to bar Burnham.
While a by-election defeat in a formerly safe seat would not be unheard of for a governing party, it would raise the political stakes even further for Sir Keir ahead of the May elections, where the Scottish and Welsh parliaments as well as some councils in England are being contested.
There is a widespread expectation among Labour MPs that at least some of their number would respond to a bad set of results by trying to force a leadership contest.
