History of challenges to Conservative leaders
Theresa May is not the first Conservative leader to vow to fight to save her position in the face of rebellious MPs.
Margaret Thatcher famously declared “I fight on, I fight to win” as she battled a challenge from Michael Heseltine in 1990, only to stand down after senior Tories advised her she was heading for defeat.
Lady Thatcher is the only Prime Minister to be removed from office by a party leadership ballot among her own MPs.
Under the different rules in place in 1990, Mrs Thatcher defeated Mr Heseltine by 204 to 152 in a vote of Tory MPs after he challenged her position.
But she failed to achieve the 15% margin of victory to prevent a second-round ballot.
Despite her defiant statement that she would fight on, she withdrew from the contest two days later after a succession of Cabinet ministers told her they thought she would lose. Her departure allowed John Major to come through and defeat Mr Heseltine for the leadership.
Mr Major himself called a “back-me-or-sack-me” contest in 1995, resigning as leader to fight for the job after coming under pressure from rebels over Europe.
He easily saw off his challenger John Redwood by 218 votes to 89 and went on to lead the Tories into the 1997 general election, resigning after his landslide defeat by Tony Blair.
Party rules had changed by the time of the next challenge to a Tory leader, requiring Iain Duncan Smith to face a confidence vote after MPs submitted letters to the chair of the backbench 1922 Committee in 2003.
He lost the vote by 90-75 and resigned shortly afterwards, clearing the way for Michael Howard to take over as leader without a ballot, after no other contenders stood against him.
Mr Howard himself eventually stood down voluntarily as leader after losing the 2005 general election, as did David Cameron after losing the 2016 EU referendum and William Hague after the 2001 general election.
Edward Heath stayed on as Tory leader after losing power in 1974 but was forced out by Mrs Thatcher in a leadership contest the following year.