Two government sources told BuzzFeed News they think it is now an inevitability that the threshold will be reached at some point over the next few weeks, before May is able to strike a Brexit deal with the EU.

Two of the Tory MPs who told colleagues they have submitted letters in the last few days are Brexiteers. One said they had received pressure from their local Conservative association to write a letter. They had both previously said they would not vote for a deal based on the PM’s Chequers proposals.

But two MPs are Remainers. One told friends they think Chequers is “the worst of all worlds” and that they want a second referendum to allow the public to decide between a clean break from the EU or remaining as a member.

The other, BuzzFeed News understands, believes the Tory party brand is being permanently damaged by May’s leadership.

The revelation that both Leave and Remain MPs have submitted letters shows the concerns are not just about May’s handling of the Brexit negotiations, MPs said.

One told BuzzFeed News: “For some of us this really isn’t all to do with Brexit. I’m worried about the state of the Conservative party under Theresa May and it is obvious she intends to go on and on — unless she is stopped.