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 in Downing Street, Mrs May said she had “done my best” to honour the 2016 EU referendum result.
It would remain a matter of “deep regret” that she had been unable to deliver Brexit, she added.
But a new PM was “in the best interests of the country”.
Mrs May said she will continue to serve as prime minister while a Conservative leadership contest takes place.
She will step down as Tory leader on 7 June and a leadership contest is due to begin the following week.