Theresa May has said she will quit as Conservative leader on 7 June, paving the way for a contest to decide a new prime minister.
In an emotional statement, she said she had done her best to deliver Brexit and it was a matter of "deep regret" that she had been unable to do so.
Mrs May said she would continue to serve as PM while a Conservative leadership contest takes place.
The party said it hoped a new leader could be in place by the end of July.
It means Mrs May will still be prime minister when US President Donald Trump makes his state visit to the UK at the start of June.
Mrs May announced she would step down as Tory leader on 7 June and had agreed with the chairman of Tory backbenchers that a leadership contest should begin the following week.
On Friday, Foreign Secretary Jeremy Hunt became the latest MP to say that he would run for the party leadership, joining Boris Johnson, Esther McVey and Rory Stewart, who had already confirmed their intentions. More than a dozen others are believed to be seriously considering entering the contest.
The prime minister has faced a backlash from her MPs against her latest Brexit plan, which included concessions aimed at attracting cross-party support.
Andrea Leadsom quit as Commons leader on Wednesday saying she no longer believed the government's approach would "deliver on the referendum result".
