Theresa May has said she will quit as Conservative leader on June 7, 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.
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 May will still be prime minister when US President Donald Trump makes his state visit to the UK at the start of June.
May announced she would step down as Tory leader on June 7 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”.
May met Home Secretary Sajid Javid and Foreign Secretary Jeremy Hunt at Downing Street on Thursday where they are understood to have expressed their concerns about her proposed withdrawal bill.
In her statement on Friday, she said she had done “everything I can” to convince MPs to support the withdrawal deal she had negotiated with the European Union but it was now in the “best interests of the country for a new prime minister to lead that effort”.
She added that, in order to deliver Brexit, her successor would have to build agreement in Parliament.
“Such a consensus can only be reached if those on all sides of the debate are willing to compromise,” she said.
May’s voice shook as she ended her speech saying: “I will shortly leave the job that it has been the honour of my life to hold.
“The second female prime minister, but certainly not the last.
“I do so with no ill will, but with enormous and enduring gratitude to have had the opportunity to serve the country I love.”
In a statement, the Conservative Party said the likely timetable for the party leadership contest was that nominations would close during the week beginning 10 June, with the process of whittling down candidates to the final two to conclude by the end of the month.
Those names would then be put to a vote of party members before the end of July.
Labour Leader Jeremy Corbyn said she had been “right to resign” and that the Conservative Party was now “disintegrating”.
May’s predecessor, David Cameron – who resigned as PM after campaigning for Remain and losing the referendum – said she should be thanked for her “tireless efforts”.
He added: “I know how painful it is to accept that your time is up and a new leader is required.
“She has made the right decision – and I hope that the spirit of compromise is continued.”
