Theresa May’s two closest advisers have quit after the Conservatives’ failure to win the general election.
The BBC understands the PM had been warned she faced a leadership challenge on Monday unless she sacked Nick Timothy and Fiona Hill.
Mr Timothy said he was taking responsibility for his role in the “disappointing” election result.
He said he regretted not including a pledge to cap social care costs in the party’s widely criticised manifesto.
The BBC’s assistant political editor Norman Smith said the pair’s departure bought the PM some “breathing space” following 24 hours of recriminations after the Conservatives lost their overall majority.
He said the two were so close to the PM that critical MPs believed that, unless they made way, she would not be able to change her leadership style to adopt a more “outgoing, inclusive, responsive, empathetic approach”.
Mrs May has said she intends to stay as prime minister and is seeking support for the Democratic Unionists to form a government. Chief Whip Gavin Williamson is in Belfast to begin formal talks on a deal.
Mr Timothy and Ms Hill both stepped down amid mounting pressure on Mrs May to overhaul the way No 10 worked and broaden her circle of advisers.
Announcing his resignation on the Conservative Home website, Mr Timothy urged Tory MPs to “get behind” Mrs May but said nothing should be allowed to get in the way of the process of forming a government and beginning Brexit talks.
He said the Conservatives’ failure to win was not due to a lack of support for Theresa May and the Conservatives but due to an “unexpected surge” of support for Labour.
He conceded his party had failed to communicate a sufficiently “positive” message to voters and address their concerns over years of austerity and inter-generational divisions, including over Brexit.
“We were not talking to the people who decided to vote for Labour,” he said.
He defended the party’s “honest and strong” manifesto, saying controversial proposals on social care had been discussed in government for months and were not his own personal “pet project”.
But he added he took “responsibility for my part in this election campaign, which was the oversight of our policy programme” and “I regret the decision not to include in the manifesto a ceiling as well as a floor in our proposal to help meet the increasing cost of social care”.
Norman Smith said he understood that senior Conservatives had warned the PM they would instigate a leadership contest at a meeting of backbenchers early next week if the pair did not leave, and were confident they could get the required 48 signatures to trigger a contest.
One former minister, Anna Soubry, welcomed the clearout, saying it was the “right thing to do” and saying the PM must “build a consensus” on Brexit and other issues.
But Labour’s deputy leader Tom Watson said the PM’s advisers had “taken the fall” for her but tweeted the PM was “responsible for her own defeat”.
- Davidson: ‘No plans for breakaway party’
- Welsh MPs wait on Tory reshuffle news
Earlier, Mrs May’s director of communications until the election was announced, Katie Perrior, called the campaign “pretty dysfunctional”, telling the BBC she “needed to broaden her circle of advisers and have a few grey hairs in there who been around a bit and could say ‘don’t do that'”.
As the Conservative leadership begins formal negotiations with the DUP, disquiet is being expressed in some quarters about the move.
Charles Tannock, a Conservative member of the European Parliament, said the DUP was a “hardline, populist, protectionist” party and a “poor fit” as a partner for the Conservatives.
The leader of the Scottish Conservatives, Ruth Davidson, tweeted a link to a speech she had made about same-sex marriage – something the DUP opposes.
Northern Ireland is the only part of the UK where same-sex marriage is not legal.
Ms Davidson, who is gay, plans to marry her partner in the near future and said she had been “straightforward” with Mrs May about her concerns.
“I told her that there were a number of things that count to me more than the party,” she told the BBC. “One of them is country, one of the others is LGBTI rights.
“I asked for a categoric assurance that if any deal or scoping deal was done with the DUP, there would be absolutely no rescission of LGBTI rights in the rest of the UK, in Great Britain, and that we would use any influence that we had to advance LGBTI rights in Northern Ireland.”
By winning 12 additional seats in Scotland, Ruth Davidson played a significant part in helping Theresa May to stay in Downing Street, BBC Scotland editor Sarah Smith says.
Speaking on Friday, the prime minister said her party had a “strong relationship” with the DUP and that she intended to form a government which could “provide certainty and lead Britain forward at this critical time for our country”.
DUP will use leverage on May deal
Analysis by political correspondent Gary O’Donoghue
The clock is ticking for Theresa May. She needs to conclude a deal with the DUP in the next week or so ahead of the Queen’s Speech, which will set out the new government’s agenda.
That takes place on Monday 19 June – the same day Brexit negotiations are due to start.
The DUP and its 10 MPs are in a very strong position. It’s all their Christmases rolled into one and they will make sure they leverage as much as they can from their advantage.
Money for Northern Ireland will undoubtedly be part of their demands, and Mrs May will expect that. But trickier will be any demands they have about the implementation of Brexit in Northern Ireland – in particular the DUP’s determination to maintain a soft border with the south.
Another potential problem is the planned restart of negotiations for power-sharing in the province.
Typically the British government tries to act as an honest broker between Republicans and Unionists. But if Mrs May is doing a deal with the DUP, that could make it harder to reach an agreement with Sinn Fein.
- Who are the DUP’s 10 MPs?
DUP leader Arlene Foster confirmed she had spoken to Mrs May and that they would speak further to “explore how it may be possible to bring stability to this nation at this time of great challenge”.
Mrs May is expected to continue assembling her top team later after she decided to keep key figures – including Chancellor Philip Hammond, Foreign Secretary Boris and Home Secretary Amber Rudd – in their current roles.
David Davis will also stay on as Brexit secretary and Sir Michael Fallon will keep his role as defence secretary.
There could be limited changes elsewhere in the cabinet while nine middle-ranking and junior ministers, including Ben Gummer and Jane Ellison, lost their seats at the general election and will need to be replaced.
Jeremy Corbyn has said Mrs May should “make way” for a government that would be “truly representative of the people of this country”.
The Labour leader, who is expected to announce his shadow cabinet on Sunday, said his party was ready to form a minority government of its own, but stressed he would not enter into any “pacts or deals” with other parties.
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