Boris Johnson has become Prime Minister after accepting an invitation from the Queen to form a new government.
Mr Johnson used his first speech to insist that Brexit will be delivered, and that he will give the country “the leadership it deserves”.
Speaking outside 10 Downing Street, the Tory leader said he would meet the October 31 deadline “no ifs or buts”.
Watched by girlfriend Carrie Symonds, Mr Johnson promised he would “change this country for the better”.
Theresa May earlier visited Buckingham Palace to tender her resignation.
Here’s the latest from Westminster…
Home Secretary Sajid Javid has entered Number 10 Downing Street.
Watch: Boris Johnson arrives at Number 10.
Jeremy Corbyn has said that Boris Johnson will be unable to honour his commitment to deliver Brexit by the end of October.
“I don’t see how he can,” he said.
“All he did today was a lot of bluff about delivering it and a whole load of stuff about the social issues in Britain – of which there are serious problems, most of which he was party to the the creation of.
“He has then offered tax cuts to the very richest which isn’t going to solve any of the problems he outlined.
“We certainly do need something much more serious in our approach to Europe as well as to the problems of inequality in this country.”
Northern Ireland Secretary Karen Bradley said she has left the Government.
After Daily Mail journalist John Stevens tweeted that Caroline Nokes had been sacked, the immigration minister responded saying: “Good of you to tell me first.”
Transport Secretary Chris Grayling has resigned, a source said.
Housing, Communities and Local Government Secretary James Brokenshire has said on Twitter that he will be leaving the Government.
Education Secretary Damian Hinds confirmed he was also leaving the Government.
Liam Fox and Greg Clark have also announced their departures from government.
Defence Secretary Penny Mordaunt has said she is leaving the Government and returning to the backbenches.
There was a warm welcome for Boris Johnson inside Number 10.
Age UK was “hugely encouraged” by Mr Johnson’s pledge to fix the social care crisis.
Caroline Abrahams, charity director at Age UK and the co-chair of the Care and Support Alliance (CSA), said: “We are hugely encouraged that within a few minutes of taking office our new Prime Minister has pledged to fix the crisis in social care.
“It also means that the debate can shift from ‘if’ to ‘how’.
“Putting the right policies in place will be crucial and Age UK and the CSA looks forward to engaging with the new Government on what needs to be done.
“If Mr Johnson can make good on his pledge he will deserve the heartfelt thanks of millions of disabled adults, older people and their carers, right across the country.”
But Scottish First Minister Nicola Sturgeon was less impressed.
A number of Conservative MPs congratulated the new Prime Minister on his maiden speech.
Shadow Brexit secretary Sir Keir Starmer has said the UK is in a “Brexit crisis” and that Boris Johnson’s premiership will make situations worse for communities “devastated by nine years of Tory austerity”.
Mr Johnson said under “any circumstances” the UK would need to get ready to come out of the EU customs union and regulatory control.
“Fully determined at last to take advantage of Brexit, because that is the course on which this country is now set,” he said.
“With high hearts and growing confidence we will now accelerate the work of getting ready.
“And the ports will be ready and the banks will be ready and the factories will be ready and business will be ready and the hospitals will be ready and our amazing food and farming sector will be ready and waiting to continue selling ever more, not just here but around the world.
“And don’t forget that in the event of a no-deal outcome we will have that extra lubrication of the £39 billion and whatever deal we do we will prepare this autumn for an economic package to boost British business and to lengthen this country’s lead as the number one destination in this continent for overseas investment.”
Mr Johnson said he would be Prime Minister of the whole UK, stating: “It is time we unleashed the productive power, not just of London and the South East, but of every corner of England, Scotland, Wales and Northern Ireland.
“The awesome foursome that are incarnated in that red, white and blue flag.”
Mr Johnnson said work would begin to recruit 20,000 additional police officers “to make your streets safer”.
Work would also start on 20 new hospital upgrades, ensuring additional funding for the NHS reached the front line.
Mr Johnson also vowed to fix the “crisis” in social care “once and for all” with a clear plan to give every older person the dignity and security they deserve.
He said the Government would also “level up” funding for primary and secondary schools to ensure all pupils received a “superb education wherever they are”.
Mr Johnson said he was “convinced we can do a deal” to resolve the issue of the Irish border but he would prepare for a no-deal Brexit.
He said: “I will take personal responsibility for the change I want to see.
“Never mind the backstop, the buck stops here.”
Mr Johnson said that he will succeed in delivering Brexit by the Halloween deadline “no ifs or buts”.
“The people who bet against Britain are going to lose their shirts because we are going to restore trust in our democracy,” he said.
“And we are going to fulfil the repeated promises of Parliament to the people and come out of the EU on October 31 no ifs or buts.
“And we will do a new deal, a better deal that will maximise the opportunities of Brexit while allowing us to develop a new and exciting partnership with the rest of Europe based on free trade and mutual support.
“I have every confidence that in 99 days time we will have cracked it.
“But you know what we aren’t going to wait 99 days because the British people have had enough of waiting.
“The time has come to act, to take decisions to give strong leadership and to change this country for the better.”
New Prime Minister Boris Johnson said he had accepted the Queen’s invitation to form a Government and paid tribute to Theresa May as he spoke in Downing Street.
“I pay tribute to the fortitude and patience of my predecessor and her deep sense of public service, but in spite of all her efforts, it has become clear that there are pessimists at home and abroad who think after three years of indecision that this country has become a prisoner to the old arguments of 2016 and in this home of democracy we are incapable of honouring a democratic mandate.
“And so I am standing before you today, to tell you the British people, that those critics are wrong – the doubters, the doomsters, the gloomsters are going to get it wrong again.”
Prime Minister Boris Johnson has arrived in Downing Street.
The Archbishop of Canterbury, Justin Welby, has offered prayers for Boris Johnson after the Tory leader was invited to become Prime Minister by the Queen.
European Council President Donald Tusk offered his congratulations.
Boris Johnson has left Buckingham Palace after an audience with the Queen and is travelling to Downing Street where he will make his first speech as Prime Minister.
Mr Johnson’s girlfriend, Carrie Symonds, is stood with members of his team outside Number 11 as they wait the arrival of the new Prime Minister at Downing Street.
Boris Johnson has officially become Prime Minister after accepting an invitation from the Queen to form a government.
Mr Johnson will shortly head to 10 Downing Street.
Watch: Theresa May gives final speech as PM
Labour MP Jess Phillips joked: “No one is in charge for the next 15 mins so I’m going to suggest we immediately instigate actions to act on the climate crisis, set up a proper costed funding system for social care free at the point of delivery and quickly sign off the building of millions of social homes.”
Greenpeace has claimed the protest on the Mall which blocked Boris Johnson’s route to Buckingham Palace to meet the Queen.
The UK branch of the group tweeted: “BREAKING: we just tried to hand the incoming PM a crucial letter – it contains the answers to tackling the Climate Emergency.
“But will he *act*?”
Boris Johnson has arrived at Buckingham Palace for an audience with the Queen and is minutes away from becoming the next Prime Minister.
Mr Johnson stepped from his chauffeur-driven limousine without his girlfriend Carrie Symonds and was welcomed by the Queen’s private secretary and her equerry.
And like Mrs May, he too was cheered by a group of visitors touring the summer opening of Buckingham Palace, and he waved in response.
Climate protesters briefly blocked the route of Boris Johnson as he was driven down the Mall to Buckingham Palace to meet the Queen.
Climate protesters wearing red T-shirts sought to form a human chain across the Mall as Mr Johnson was driven towards Buckingham Palace.
Mr Johnson’s vehicle appeared to stop briefly as it met the protest, before continuing to the palace.
Theresa May has tendered her resignation as prime minister to the Queen which “Her Majesty was graciously pleased to accept”, Buckingham Palace said.
As Mrs May arrived at Buckingham Palace, her outgoing chief whip Julian Smith tweeted an image of the letter he was handing his replacement, Sherwood MP Mark Spencer, with the words: “Good luck!”
Mrs May will tender her resignation as prime minister during her audience with the Queen.
By convention the Queen is above party politics and does not personally choose the next prime minister, so Mrs May’s last duty will be to tell the head of state which person has enough support to form the next government – Boris Johnson.
The meeting was held in the Queen’s audience room in the monarch’s private apartments.
Mr May will wait until the end of the audience before joining the Queen and his wife.
Watch: Theresa May’s key moments
Theresa May was warmly greeted when she arrived at Buckingham Palace for her final audience as Prime Minister with the Queen.
Edward Young, the Queen’s private secretary, and Major Nana Kofi Twumasi-Ankrah, the monarch’s equerry, were waiting to welcome the outgoing premier and shook her hand as she stepped from her chauffeur-driven limousine.
She was joined by her husband Philip who also shook hands with the royal aides.
The ministerial vehicle had swept across the gravel of the palace’s quadrangle and stopped at the King’s Door entrance of the monarch’s official London residence.
As Mrs May emerged from the car a group of visitors, touring the summer opening of Buckingham Palace, gave a cheer and the politician turned and waved.
Lady Susan Hussey, one of the Queen’s ladies-in-waiting, was standing in the doorway and kissed Mrs May on both cheeks and shook hands with her husband before they were ushered inside.
During Mrs May’s farewell statement as prime minister a shout of “no Brexit” could be heard coming from outside Downing Street.
Mrs May responded saying: “I think the answer to that is – I think not.”
Mrs May stated: “Finally, and most of all, I want to thank my husband Philip who has been my greatest supporter and my closest companion.”
Mrs May said the “immediate priority” was to deliver Brexit for benefit of the nation and to move the UK away from the “current impasse”.
“The immediate priority being to complete our exit from the European Union in a way that works for the whole United Kingdom,” she said.
“With success in that task can come a new beginning for our country, a national renewal that can move us beyond the current impasse into the bright future the British people deserve.
“To serve as Prime Minister of the United Kingdom is the greatest honour. The heavy responsibilities are outweighed by the huge potential to serve your country. But you achieve nothing alone.”
She thanked staff and colleagues in Parliament, as well as service personnel and public servants across the nation.
“All are inspired by the noble wish to serve their country in the national interest,” she said.
Mrs May said she hoped that young girls seeing a female prime minister would realise “there are no limits to what you can achieve”.
She said the economy had been restored, public services reformed and values defended on the world stage during her time in office.
“Of course much remains to be done. The immediate priority being to complete our exit from the European Union in a way that works for the whole United Kingdom.”
Mrs May, speaking outside Number 10 with her husband Philip, 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.”
Theresa May said she wanted a Brexit “that works for the whole United Kingdom” as she delivered her farewell speech outside Number 10.
David Lidington, effectively Theresa May’s deputy prime minister, has confirmed he is leaving the Government saying “it’s the right moment to move on”.
David Gauke said he resigned as Justice Secretary because he cannot support Boris Johnson in his “do or die” commitment to leave the EU by October 31.
He said he strongly supported Theresa May’s efforts to “deliver a smooth and orderly” Brexit and her move not to defy Parliament by leaving without a deal before the March 29 deadline.
“Of course, we will now have a new Prime Minister and I join you in wishing Boris Johnson well,” he wrote.
“I very much hope he will achieve his objective of concluding a deal with the EU that Parliament will support.
“In my view, the only responsible way to honour the 2016 referendum result is to leave the EU with a deal and, without such a deal, I fear for the prosperity, security and unity of the United Kingdom.
“Given Boris’s stated policy of leaving the EU by October 31 at all costs, I am not willing to serve in his Government. I believe I can most effectively make the case against a no-deal Brexit from the backbenches.”
The chief whip in the Lords, Lord Taylor of Holbeach, is also standing down.
A source said this had been long planned and was not to do with the “political situation”.
“He has been on the front bench for a long time,” the source said.
A crowd has gathered outside Downing Street ahead of Theresa May’s departure.
Former prime minister David Cameron has tweeted his congratulations to the new Conservative leader, Boris Johnson.
Jeremy Corbyn’s spokesman said Theresa May was “well off-beam” in her call for the Labour leader to quit.
“She was failing to remember that she became Prime Minister on the basis of no mandate at all, she was elected by nobody, as has her successor been in terms of the public,” the spokesman said.
“Jeremy has been elected as leader of the Labour Party twice on large majorities. In the case of his last election, I think his opponent (Owen Smith) got substantially more votes than Boris Johnson got in the Tory leadership election.
“In the 2017 election he presided over a campaign which delivered the largest increase in the Labour vote since 1945. So I think she’s well off-beam there.”
Justice Secretary David Gauke has also resigned from Government, a source confirmed.
International Development Secretary Rory Stewart – who ran for the leadership – has resigned.
Watch: Philip Hammond resigns:
Health Secretary Matt Hancock has thanked Mrs May for her “endless integrity” on her final day in office.
The Chancellor Philip Hammond has resigned ahead of Boris Johnson taking over as Prime Minister.
Theresa May has arrived back at Downing Street.
She is now expected to give a private farewell to staff before addressing the nation for one final time as PM before heading to Buckingham Palace to see the Queen and offer her resignation.
Before her farewell speech, Mrs May will have a private lunch in the Number 10 garden with her husband Philip.
Watch: Theresa May tells Jeremy Corbyn he should quit too
In her final remarks, Mrs May said: “We are living through extraordinary political times. This House of Commons is rightly at the centre of those events.
“That’s because of the vital link between every single member of this House and the communities, the Commons that we represent.
“That’s the bedrock of our parliamentary democracy and of our liberty.
“And each of us, wherever we sit and whatever we stand for, can take pride in that.”
The Prime Minister’s voice faltered as she made her final remarks: “That duty to my constituents will remain my greatest motivation.”
As she left the despatch box for the final time, many fellow MPs from across the House stood and applauded Mrs May – which is a break in usual Commons convention.
Tory MPs were joined by the DUP and Lib Dems in giving Mrs May the standing ovation.
Some Labour backbench MPs also applauded, but Mr Corbyn did not.
In her final remarks at the despatch box, the Prime Minister said she believes there will be another woman prime minister among the current cohort of MPs.
She added: “I’m sure that amongst the women in this House today there is a future prime minister, maybe more than one.
“Later today I will return to the backbenches and it will be my first time in 21 years so it’s going to be quite a change from standing here at the despatch box.
Mrs May also said that she had been told she had answered 4,500 questions over 140 hours in the House, “more than I might have expected”.
New Liberal Democrat leader Jo Swinson said it was inspiring for girls in her East Dunbartonshire constituency to see women in positions of power, whether as First Minister of Scotland or Prime Minister.
She said: “Can I ask the Prime Minister what advice she has for women across the country on how to deal with those men who think they could do a better job but are not prepared to do the actual work?”
Mrs May replied: “My advice to all women is actually be true to yourself, persevere, keep going and be true to the vision you’re working for.”
She then noted all parties sitting in the Commons have had a female leader bar Labour, saying: “We almost have a full set.
“My party has had two women leaders, the Liberal party now has a woman leader, the SNP has a woman leader as do the DUP, Plaid and the Greens have – even the Independent Tigger Group Change UK – or whatever they’re calling themselves this week – are now on to their second woman leader.
“There’s only one party in this House letting the side down – the Labour Party.”
The Prime Minister paid tribute to her husband Philip May, who was watching her final Commons exchange from the gallery.
Tory MP Keith Simpson (Mid Norfolk) praised Mr May’s support of his wife, adding: “For many of us our husbands, wives, partners are the unsung heroes.”
Mrs May replied: “I am taking a lead from you Mr Speaker in saying that I am very pleased to be able to see my husband in the gallery”.
Mr Blackford also raised questions over Mrs May’s confidence in her successor, saying: “The burdens of office are considerable, the loneliness of leadership can be stark. Whilst there are times we have clashed on points of political difference, equally we have stood together when it has been right to do so.
“As the Prime Minister departs, is she confident that the office of Prime Minister can be upheld by her flagrant successor?”
Mrs May responded: “Yes, I congratulate (Mr Johnson) for winning the Conservative leadership election, he will take over as Prime Minister and I look forward to a first class Conservative Government under his leadership delivering for the whole of the UK.”
SNP Westminster leader Ian Blackford said he had tabled a cross-party early day motion rejecting any prorogation of Parliament, and urged Theresa May to sign it to stop the suspension of proceedings “under any circumstances”.
The party’s chief whip Patrick Grady tweeted a copy of the motion, which had been co-signed by Liberal Democrats leader Jo Swinson, Plaid Cymru Westminster leader Liz Saville Roberts and Green Party MP Caroline Lucas.
Concluding her final exchange with Mr Corbyn, the Prime Minister paid tribute to his constituency work but called for him to consider resigning.
She said: “It is the strength of our British democracy that the Prime Minister and the Leader of the Opposition have these exchanges across the despatch boxes every week at two swords’ length.
“No quarter is sought and none is given, and that is as it should be in our adversarial parliamentary democracy.”
Mrs May added: “One thing we both have in common is a commitment to our constituencies, I saw that after the terrorist in Finsbury Park Mosque in his constituency.
“Perhaps I could just finish my exchange with him by saying this: As a party leader who has accepted when her time was up, perhaps the time is now for him to do the same?”
Mr Corbyn called for Boris Johnson to call a general election upon entering Number 10 to “let the people decide their future”.
“Given her successor has no mandate from the people, no mandate in which to move into office, doesn’t she agree the best thing the right honourable member for Uxbridge could do later on today when he takes office is to call a general election and let the people decide their future?”
SNP Westminster leader Ian Blackford followed and also said the Mr Johnson has “no mandate” from the people of Scotland.
Labour leader Jeremy Corbyn said: “Today marks the final day in office for the Prime Minister and I pay tribute to her sense of public duty – public service should always be recognised.
“Being an MP, minister or indeed a prime minister is an honour that brings with it huge responsibility and huge pressures both personally and, I’m sure the Prime Minister and the whole House will agree, on those very closest to us, who often are not able to answer back for the criticisms made against them.
“So I hope she has a marginally more relaxing time on the backbenches and perhaps, like the Chancellor, even helping me to oppose the reckless plans of her successor.”
As MPs laughed, Mr Corbyn noted the Tories were in “such good heart”, adding: “For tomorrow they won’t be.”
Mrs May said: “I am pleased to hand over to an incoming leader of the Conservative Party and Prime Minister who I worked with when he was in my Cabinet, and who is committed as a Conservative who stood on a Conservative manifesto in 2017 to delivering on the vote of the British people in 2016 and to delivering a bright future for this country.”
Theresa May is at the despatch box outlining her daily schedule, including her meeting with the Queen later.
She said: “This morning I had meetings with ministerial colleagues and others.
“Following my duties in this House this afternoon I shall have an audience of Her Majesty the Queen.
“I shall then continue with my duties in this House from the back benches where I will continue to be the member of parliament for Maidenhead.”
Theresa May arrived in the Commons chamber to cheers from Tory backbenchers ahead of her final Prime Minister’s Questions.
She took her seat next to Chancellor Philip Hammond.
Theresa May’s husband Philip is in the gallery of the House of Commons to watch his wife’s final session of Prime Minister’s Questions at noon.
Theresa May has left Downing Street to be driven to the House of Commons for her final stint at the despatch box for Prime Minister’s Questions.