Boris Johnson quit as Conservative Party leader after admitting he failed to persuade Cabinet colleagues that he could fight on in office.
The Prime Minister said it was "eccentric" to change governments at this stage but "I regret not to have been successful in those arguments".
A new Tory leader will now be elected who will replace Johnson in No 10.
During a six-minute speech in Downing Street Johnson said he didn't want to leave office but it was the will of his party that he should resign.
Here is Boris Johnson's speech in full:
“Thank you, thank you! It is clearly now the will of the Parliamentary Conservative party that there should be a new leader of that party and therefore a new prime minister.
“And I’ve agreed with Sir Graham Brady, the chairman of our back bench MPs, that the process of choosing that new leader should begin now. The timetable will be announced next week and I’ve today appointed a Cabinet to serve, as I will, until a new leader is in place.
“So I want to say to the millions of people who voted for us in 2019, many of them voting Conservative for the first time, thank you for that incredible mandate, the biggest Conservative majority since 1987, the biggest share of the vote since 1979.
“And the reason I have fought so hard in the last few days to continue, to deliver that mandate in person, was not just because I wanted to do so but because I felt it was my job, my duty, my obligation to you, to continue to do what we promised in 2019.
“And of course I’m immensely proud of the achievements of this government, from getting Brexit done to settling our relations with the continent for over half a century.
“Reclaiming the power for this country to make its own laws in Parliament. Getting us all through the pandemic. Delivering the fastest vaccine rollout in Europe, the fastest exit from lockdown, and in the last few months, leading the West in standing up to Putin’s aggression in Ukraine.
“And let me say now 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. At the same time, in this country, we’ve been pushing forward a vast programme of investment, in infrastructure and skills and technology, the biggest in a century.
“Because if I have one insight into human beings it is that genius and talent and enthusiasm, imagination, are evenly distributed throughout the population but opportunity is not.
“And that’s why we must keep levelling up, keep unleashing the potential of every part of the UK. And if we can do that in this country we will be the most prosperous in Europe.
“In the last few days I’ve tried to persuade my colleagues that it would be eccentric to change governments when we’re delivering so much, when we have such a vast mandate and when we’re actually only a handful of points behind in the polls.
“Even in mid-term after quite a few months of pretty relentless sledging and when the economic scene is so difficult domestically and internationally. I regret not to have been successful in those arguments and of course it’s painful not to be able to see through so many ideas and projects myself.
“But as we’ve seen at Westminster the herd instinct is powerful and when the herd moves it moves, and my friends in politics no one is remotely indispensable.
“Our brilliant and Darwinian system will produce another leader equally committed to taking this country forward through tough times, not just helping families to get through it but changing and improving the way we do things.
“Cutting burdens on businesses and families and yes, cutting taxes, because that is the way to generate the growth and the income we need to pay for great public services.
“And to that new leader, whoever he or she may be, I say I will give you as much support as I can. And to you the British public - I know there will be many people who are relieved and perhaps quite a few who will also be disappointed.
“And I want you to know how sad I am to be giving up the best job in the world. But them’s the breaks.
“I want to thank Carrie and our children, all the members of my family who have had to put up with so much for so long.
“I want to thank the peerless British civil service for all the help and support you’ve given, our police, our emergency services, and of course our fantastic NHS who at a critical moment helped to extend my own period in office.
“As well as our armed services and our agencies that are so admired around the world, and our indefatigable Conservative Party members and supporters whose selfless campaigning makes our democracy possible.
“I want to thank the wonderful staff here, at Chequers, here at No10, and our fantastic prop force detectives - the one group, by the way, who never leak.
“Above all I want to thank you, the British public, for the immense privilege you have given me. And I want you to know that from now on until the new Prime Minister is in place, your interests will be served and the government and the country will be carried on.
“Being Prime Minister is an education in itself. I've traveled to every part of the UK.
“And in addition to the beauty of our natural world I've found so many people possessed of such boundless British originality, and so willing to tackle old problems in new ways, I know that even if things can sometimes seem dark now, our future together is golden.
“Thank you all very much.”
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