Allies of Ms May were unceremoniously cleared out, with rival Jeremy Hunt was among the senior figures to leave the government in favour of Brexiteers.
Sajid Javid was appointed as chancellor, with Brexiteers Priti Patel and Dominic Raab returning to the cabinet as home secretary and foreign secretary.
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Welcome to The Independent's politics liveblog - today Boris Johnson will enter Downing Street, replacing Theresa May as prime minister.
He is expected to launch a bid to broaden his appeal by using his first day in office to appoint women and ethnic minority MPs to what aides were terming a “cabinet for modern Britain”.
The shake-up is expected to include a return to the cabinet for Priti Patel, 20 months after she was forced to resign after she was revealed to have set up secret back-channel negotiations with the Israeli government, as well as promotions for rising stars from across different wings of the party.
After his landslide victory in the Tory leadership race, Mr Johnson faces an urgent need to shore up the party’s position, with his wafer-thin working majority expected to be reduced to just one after next week’s Brecon and Radnorshire by-election.
Responding to US President Donald Trump's statement that Mr Johnson and Brexit Party leader Nigel Farage would work well together, Mr Hancock told the BBC: "There is no way that we are going to have any kind of electoral pact with the Brexit Party and with Nigel Farage."
Writing in the Daily Telegraph today, Mr Farage claims: "[Mr Johnson] is going to have to risk his longed-for position as PM to ensure Brexit is enacted properly."
He continued: "The inescapable truth, therefore, is that he must hold an autumn general election. That is his only way out .. [and] for this strategy to work, he will need the support of the Brexit Party.
"If he is able to convince us, then together we would electorally smash the Labour Party, he would assume a big working majority, and he would go down as one of the great leaders in British history."
Boris Johnson last night appointed one of Sky’s senior executives as his business adviser, just days after it emerged the multi-millionaire had lent his £9.5m Westminster flat to the incoming prime minister.
As the newly-appointed Tory leader prepared to unveil his top team on Wednesday, it emerged Andrew Griffith, a chief finance director at the broadcaster, will enter Downing Street with Mr Johnson.
Labour immediately seized on the appointment, saying: “The public would be forgiven for coming to the conclusion that Johnson’s friends can buy influence with the new administration.”
Ian Blackford, the SNP leader at Westminster, told the BBC Radio 4's Today programme: "I think as it stands today he could be the last prime minister of the United Kingdom".
His warning echoes that of the former Labour prime minister Gordon Brown. who warned last week of an approaching "head on conflict" between the ex-foreign secretary's hardline views and the SNP's "extreme nationalism".
A key Boris Johnson supporter has stamped on Nigel Farage’s offer of a possible electoral pact to deliver a no-deal Brexit, insisting it will never happen.
The Brexit Party leader has renewed his suggestion of an alliance if the new prime minister calls a general election, to ensure the Commons has a majority for crashing out of the EU.
It could see the Brexit Party agree not to stand against Tory candidates committed to a no-deal, in return for the Conservatives giving Mr Farage’s party a clear run in Labour-held seats.
According to the BBC's Laura Kuenssberg, Dominic Cummings, a former chief at Vote Leave during the referendum and key adviser to Michael Gove, has been appointed as Boris Johnson's new senior adviser.
Mr Cumming's has previously written an article for the Spectator under the headline: "The ERG are Remain's useful idiots".
"Those of you in the narcissist-delusional subset of the ERG, who have spent the last three years scrambling for the 8.10am Today slot while spouting gibberish about trade and the law across SW1," he added.
Theresa May's director of communications, Robbie Gibb, has just tweeted his congratulations to Boris Johnson. He will leave Downing Street today alongside the PM.
Europe's newspapers reacted with a mixture of disbelief, mockery, and depression at the news that Boris Johnson is to become British prime minister.
In a strident editorial the Irish Times refers to Mr Johnson's victory as "a new nadir" for the UK. The newspaper warned that the best hope for Ireland, Europe and "British citizens themselves - is that Johnson as prime minister will be guided by three of his worst traits, which together have defined his career: he doesn't mean a word he says, he is obsessed with power and he is willing to betray those closest to him in the pursuit of that power".
Over the North Sea, leading Danish broadsheet Politiken ran a leader column claiming that like US president Donald Trump, Mr Johnson has "built his entire career on shameless lies and extreme self-promotion".
As Boris Johnson prepares to enter Downing Street, the Press Association has released some memorable photographs of past prime minister entering the famous door on the first day of their premierships.
Margaret Thatcher in 1979
John Major in 1990
Tony Blair in 1997
Gordon Brown in 2007
Theresa May in 2016
In the committee corridors of Westminster last night, a Tory MP declared the “circus has come to town” after Boris Johnson addressed the 1922 for the first time as Conservative leader.
The remarks came as Mr Johnson was greeted to the meeting with a rapturous applause and desk-thumping from Tory MPs just hours after he emerged victorious in the race to be Britain’s next prime minister.
Mr Johnson said he was “impatient” to start work, and in a message to those who did not vote for him, he added: “The love bombing starts now”.
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