Boris Johnson has announced his resignation as prime minister after less than three years in Number 10, saying: "No one in politics is remotely indispensable."

Speaking from Downing Street, he thanked the millions of people who voted Conservative at the last election, and said the reason he fought so long to remain in office was that "I thought it was my job, my duty, and my obligation to you".

He also said he had tried to persuade his cabinet it would be "eccentric" to change prime minister now, but added: "I regret not to have been successful in those arguments.

"At Westminster, the herd instinct is powerful and when the herd moves, it moves."

Mr. Johnson confirmed the process to appoint a new leader would begin now, with a timetable set out next week, yet it is still not clear exactly when he will leave Number 10 for the final time.

Earlier, a No 10 source said the PM had spoken to the chairman of the Conservative backbench 1922 Committee, Sir Graham Brady, and agreed for a new Tory leader to be in place by the party's conference in October.

But several of his MPs wanted him to leave immediately, saying after so many resignations from his government, he did not have the authority to lead.

Labour leader Sir Keir Starmer has also threatened to call a vote of no confidence in the Commons if Tory MPs cannot oust him straight away, with the support of other opposition parties.

Mr. Johnson said he was "immensely proud of the achievements of this government", pointing towards finalizing Brexit, its handling of the pandemic, and the roll our of vaccines, adding it was "painful not to see it through".

He also pledged to the people of Ukraine: "I know that we in the UK will continue to back your fight for freedom for as long as it takes."

Addressing the British public, he added: "I want you to know how sad I am to be giving up the best job in the world, but them's the breaks."

And concluding his speech, Mr. Johnson said: "I've traveled to every part of the United Kingdom and in addition to the beauty of our natural world, I find so many people possessed of such boundless British originality and so willing to tackle old problems in new ways that I know that even if things can sometimes seem dark now, our future together is golden."

There had been intense pressure on the PM to quit over the past 48 hours after more than 50 resignations from the government payroll, and waves of backbenchers appealing for him to go.

The mass rebellion began on Tuesday after Downing Street admitted the PM knew about allegations of inappropriate behavior against disgraced former Deputy Chief Whip Chris Pincher in 2019, but still appointed him in February and sent ministers out to defend him.

Health Secretary Sajid Javid and Chancellor Rishi Sunak were the first to resign on Tuesday night, but over the following days, MPs from all levels of government piled in their letters and demanded him to go.

Mr. Johnson initially insisted he was staying in post, with a source inside Number 10 saying just this morning that he planned to "fight on".

But after new education secretary, Michelle Donelan - who had only been in the post for 36 hours - resigned and his freshly appointed Chancellor Nadhim Zahawi publicly called for his exit, Downing Street confirmed the PM would be resigning today.

Labour's Sir Keir welcomed Mr. Johnson's resignation as "good news for the country", but added: "It should have happened long ago.

"He was always unfit for office. He has been responsible for lies, scandal, and fraud on an industrial scale. And all those who have been complicit should be utterly ashamed."