Prime Minister Theresa May’s two closest advisers have quit after the Conservatives failed to win a majority of MPs in the general election.
The BBC understands the PM was warned she faced a leadership challenge unless she sacked Nick Timothy and Fiona Hill.
Labour said the pair had “taken the fall” for the prime minister.
Mrs May has announced that the new Downing Street chief of staff is ex-Conservative MP and former housing minister Gavin Barwell.
Mr Timothy said he took responsibility for his role in the “disappointing” result and the widely-criticised manifesto package on social care.
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 to use the value of peoples’ homes to fund domiciliary care costs 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”.
