Theresa May on Friday announced she will step down as Conservative Party leader on June 7, with a leadership contest beginning the following week.
In a highly emotional address to the nation, she said: "I will shortly leave the job that 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."
She, however, expressed disappointment at not being able to deliver Brexit. "It is, and will always remain, a matter of deep regret to me."
May will continue as caretaker prime minister until her party elects a new leader.

Lebanese army chief and US general meet on Lebanon security
At least six dead, thousands displaced as heavy rains hit northeastern Brazil
Austrian police arrest man over poisoned baby food case
Trump not satisfied with Iran's latest proposal, will not 'leave war early'
Iran sends proposal for negotiations with US to mediator Pakistan