The existing government would have to lose the confidence of a majority of the members of the House of Commons. Then there could be an election, and if Labour w

The existing government would have to lose the confidence of a majority of the members of the House of Commons. Then there could be an election, and if Labour won that election, they could then take over. (See https://en.wikipedia.org/wiki/Motions_of_no_confidence_in_the_United_Kingdom https://en.wikipedia.org/wiki/Motions_of_no_confidence_in_th...) So it's conceivable, but not without Labour managing to jump through a fair number of constitutional hoops first.