Boris Johnson has officially been appointed prime minister of the United Kingdom, after meeting with the Queen at Buckingham Palace.
Speaking outside Downing Street, he said he would take the UK out of EU by October 31 “no ifs, no buts” and hit out at “pessimists”.
“The doubters, the doomsters, the gloomsters, they are going to get it wrong again,” he said.
“I will take personal responsibility for the change I want to see. “Never mind the backstop, the buck stops here.”
Johnson is expected to announce the members of his new cabinet this evening.
Several senior Conservatives, including chancellor Philip Hammond, resigned from the government rather than wait for Johnson to fire them.
A source close to Johnson the new prime minister would “build a cabinet showcasing all the talents within the party that truly reflect modern Britain”.
Theresa May used her farewell statement to say Johnson’s priority must be a Brexit “that works for the whole United Kingdom”.
Her speech in Downing Street was also disrupted, by a cry of “stop Brexit” from a protester outside, in reply she joked: “I think not.”
But she made clear her desire for Johnson to seek a deal with Brexit, having previously warned about the risks of a no-deal departure.
Flanked by husband Philip, she said: “I repeat my warm congratulations to Boris on winning the Conservative leadership election.
“I wish him and the government he will lead every good fortune in the months and years ahead.
“Their successes will be our country’s successes, and I hope that they will be many.”