Theresa May will be forced from office within a month if she does not set out a timetable for her departure when she meets senior backbench MPs on Thursday.

The Prime Minister will be told she faces the prospect of a confidence vote of her own MPs on June 12 if she does not agree to quit before the summer.

Mrs May has already promised to stand down once Britain has formally left the EU, but the executive of the 1922 Committee of backbench Tories will tell her on Thursday that she must agree to resign regardless of whether her Brexit deal is passed by Parliament.

There is growing unease within Tory ranks about the swift rise of Nigel Farage’s Brexit Party, which now has more than 100,000 paying supporters and is expected to dominate next week’s European elections.

Nick Timothy, Mrs May's former joint chief of staff, says it is "beyond time" for the Prime Minister "to accept that the game is up".