Firstly there is the question of how a majority is defined. This is from Smarkets:
This market will be settled based on which party (if any) wins an overall majority of the seats (50% +1) at the next UK general election. The speaker will not be counted in any party’s seat total but will be counted in the overall number of seats.
By my reckoning, this means LAB moving from the 202 seats of GE2019 to 326 which looks daunting and a fair bit higher than what will be needed for an effective majority. Because of the Sin Fein policy of not taking up their seats, this will be about 317 and would still require 115 gains which is not too far off what Tony Blair got at GE1997.
So it is quite possible that Starmer’s party could be able to form a government on something short of having an overall majority.
Also it was striking that after the local elections, John Curtice was talking in terms of Labour securing most seats but possibly some way short of a majority. The Tories did markedly better than the current Westminster polling
Of course the election could be eighteen months or so away and a lot could happen that could change everything.