Boris Johnson has said he wants to “change the country for the better” as he becomes the UK’s new prime minister.
Speaking outside Downing Street, he said the UK would leave the EU on 31 October “no ifs, no buts”, adding: “The buck stops with me.”
“The doubters, the doomsters, the gloomsters” who say it cannot be done are “wrong”, the new PM added.
Mr Johnson took over after Theresa May handed in her resignation to the Queen a short time ago.
The new PM will shortly begin putting together his cabinet – a number of Mrs May’s senior ministers have already resigned, having said they could not serve under him.
Setting out his priorities outside Downing Street, Mr Johnson hit out at the “pessimists” who do not believe Brexit can be delivered and called for an end to three years of indecision.
“The people who bet against Britain are going to lose their shirts because we are going to restore trust in our democracy,” he said.
“The time has come to act, to take decisions and change this country for the better.”
He said he had “every confidence” that the UK would leave the EU in 99 days time with a deal, but preparations for the “remote possibility” of a no-deal Brexit would be accelerated.
On the domestic front, he announced an ambitious plan to overhaul care for the elderly, reforms which have eluded previous governments because of their cost and complexity.
“We will fix it once and for all,” he insisted.
The BBC’s Vicki Young said she was struck by the ambition of Mr Johnson’s objectives beyond Brexit and the fact that he would take personal responsibility for his success or failure in achieving them.
Earlier, as she relinquished power after three years, Mrs May said being prime minister had been “the greatest honour” and wished her successor well.
In a farewell speech outside No 10, she said his government’s “successes will be our country’s successes”.
Mr Johnson’s audience with Queen Elizabeth II lasted more than half an hour.
During his journey to Buckingham Palace, his car was briefly held up by protesters from Greenpeace, who formed a human chain across The Mall.
Mr Johnson’s partner, Carrie Symonds, and key members of his staff were awaiting the new prime minister’s arrival in Downing Street.
