Nick Timothy and Fiona Hill, Theresa May’s closest advisers, have resigned in the wake of the Conservatives’ failure to win the general election.
The PM had been warned she faced a leadership challenge on Monday unless she sacked the pair, the BBC understands.
Mr Timothy said he accepted responsibility for his role in the Tory manifesto, criticized by many MPs.
He said he regretted not including a pledge to cap total social care costs.
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.
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 down to an “unexpected surge” of support for Labour and he conceded his party had failed to communicate a sufficiently “positive” message to voters and address their “frustrations” over years of austerity and inter-generational divisions, including over Brexit.
While defending the party’s manifesto, he added: “I take responsibility for my part in this election campaign, which was the oversight of our policy program.
“In particular, 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.”
Labour has urged Mrs. May to “make way” for it to form a government and she also faces criticism over the DUP deal.
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.
A number of high-profile government figures have already confirmed they are keeping their jobs in the wake of an election that saw the Tories lose 13 seats.
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'”.
Norman Smith said he understood that senior Conservatives had warned the PM they would instigate a leadership contest at a meeting of Conservative backbenchers early next week if the pair did not leave, and were confident they could get the required 48 signatures to trigger a contest.
