Boris Johnson's entry into Downing Street was foreshadowed by a series of Cabinet resignations from high-profile Tory opponents of a no-deal Brexit.
Philip Hammond quit as Chancellor, Rory Stewart resigned as International Development Secretary and David Gauke left his post as Justice Secretary in the hours before the Tory leader was to enter No 10 as prime minister.
The apparently co-ordinated resignations from Government on Wednesday came after Theresa May gave her last Prime Minister's Questions and as Mr Johnson was shaping up a Government to deliver Brexit.
The trio strongly oppose a no-deal Brexit and say they cannot support Mr Johnson's commitment to take Britain out of the EU by the deadline of October 31 "do or die".
Mr Hammond said the new PM should be "free to choose a chancellor who is fully aligned with his policy position" in his resignation letter.
And in a pointed message to Mr Johnson, he warned that the headroom built up in the public finances could only be used for tax cuts and spending boosts if a Brexit deal was secured.
Also standing down was the chief whip in the Lords, Lord Taylor of Holbeach, but a source said this was long-planned and not related to the "political situation".
The moves came as Mr Johnson was moulding his Cabinet, with a return expected for Eurosceptic Priti Patel and an advisory role for Leave campaign mastermind Dominic Cummings.
The new Tory leader will take over the reins of power after Mrs May leaves No 10 for the final time on Wednesday to formally tender her resignation to the Queen.
But even before his summons to the Palace to form a government following his resounding victory in the Tory leadership race, Mr Johnson was beginning to shape his top team.
It will include a recall to the Cabinet for Ms Patel, an ardent Brexiteer who was forced by Mrs May to resign as international development secretary over unauthorised contacts with Israeli officials.
But uncertainty surrounds the future of Mr Johnson's defeated leadership rival Jeremy Hunt after he reportedly turned down a demotion from Foreign Secretary to Defence Secretary.
One of the most eye-catching appointments expected to be made by Mr Johnson is a senior advisory role for Mr Cummings, the abrasive mastermind of the Vote Leave campaign.
Mr Cummings clashed with officials and politicians while he was an adviser to Michael Gove in the coalition government, but Mr Johnson clearly believes his forthright style will help steer Brexit through.
His appointment will be controversial given that earlier this year he was found to be in contempt of Parliament for refusing to give evidence to a committee of MPs investigating "fake news".
He is also less than impressed with the calibre of Brexiteer MPs, describing a "narcissist-delusional subset" of the European Research Group (ERG) as a "metastasising tumour" that needed to be "excised".
Mr Johnson will need the support of those same ERG hardliners for his Brexit plan.
Ms Patel has reportedly been lined up for the post of home secretary as allies said Mr Johnson was determined to create a "Cabinet for modern Britain", with a record number of ethnic minority ministers and more women attending in their own right.
It is likely to mean a promotion for the Indian-born Employment Minister Alok Sharma, who is expected to take his place around the top table.
Unlike Ms Patel, he voted Remain in the 2016 referendum but was quick to declare his support for Mr Johnson when he threw his hat into ring following Mrs May's decision to resign.
A source close to the Tory leader said: "Boris will build a Cabinet showcasing all the talents within the party that truly reflect modern Britain."
Ahead of the resignations, Mr Gauke had said there were "a few ministers leaving government today" but "some of us hope to return ... one day" in a social media post accompanied by a picture of him and Mr Stewart with artificially aged faces.
Another who may be on his way out is the Business Secretary Greg Clark, another opponent of a no-deal break.
However, Mr Johnson is likely to be faced by a gaggle of Brexiteer ministers who resigned from Mrs May's government now jostling to get back in – including Dominic Raab, Esther McVey and Andrea Leadsom.
Meanwhile, Home Secretary Sajid Javid and Treasury Chief Secretary Liz Truss were being touted as possible replacements for the key post of chancellor.
Mr Johnson has said he wants ministers who are prepared if necessary to leave the EU without a deal with Brussels.
But with a slender Commons majority for the Tories and their DUP allies of just two, he cannot afford for his government to be too narrowly-based.
Formal announcements are not expected until after Boris Johnson leaves the Palace following his audience with the Queen inviting him to form a government.
Ahead of the resignations, Mrs May used an ill-tempered set of exchanges in final Prime Minister's Question Time in the House of Commons to call on Labour leader Jeremy Corbyn to also quit his post.
After Mr Corbyn accused her of a string of policy failures and U-turns, Mrs May told the opposition leader: "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?"
Mrs May's performance was watched from the gallery by her husband Philip.
The outgoing PM is giving a final statement in Downing Street before heading to Buckingham Palace to formally resign to the Queen.
On entering Number 10, Mr Johnson will also make an address to the nation – setting out his optimistic vision for the future for a post-Brexit UK.
Allies of Mr Johnson played down the prospect of an early election or a pact with Nigel Farage's Brexit Party.