15% of Conservative MPs would need to back a no confidence vote in the PM or she would have to resign to trigger a contest.
Forty-eight Conservative MPs would need to back a no confidence vote in Theresa May to trigger a leadership contest, according to party rules.
There are two ways a contest can be triggered, most obviously if the leader of the party resigns. If they do not, 15% of Conservative MPs must write to the chairman of the 1922 committee of backbench Tories. With the party’s current crop of 317 MPs, 48 would be needed.
After David Cameron announced his resignation, five Tory MPs stood for the leadership. Unlike Labour party rules, under which candidates go to a ballot of members as long as they have the support of 15% of the party’s MPs, Conservative candidates are whittled down to a final two before party members have their say.
The ballot is based on “one member one vote”, but in 2016 one of the final two candidates, Andrea Leadsom, withdrew from the race after a damaging interview with the Times about the fact that May’s did not have children. Her withdrawal meant May was made party leader without having been elected by members.