Johnny Mercer, right, is one of the PM’s most vocal critics Dylan Martinez/PRESS ASSOCIATION

A Tory rising star today issues a call to arms for MPs to oust Theresa May, saying Britain cannot be led by someone guilty of an “abject failure to govern” at such a defining moment in our history.

Writing in The Sunday Times, Johnny Mercer says he “cannot continue to support an administration that cannot function” on issues from Brexit to the Grenfell Tower disaster and the Windrush scandal.

He spoke out as numerous Tory MPs said May was on course to face a vote of no confidence this week as all wings of the party united against her.

An ally of David Davis, the former Brexit secretary who is tipped as an interim leader, said May was entering “the killing zone”. One who hopes…