Boris Johnson’s resignation: what is going on in UK politics?

Boris Johnson, the UK prime minister, announced on Thursday that he would be stepping down as leader of the ruling Conservatives in the face of a torrent of resignations by ministers and mounting pressure from within the party.

For now he is still prime minister, but his resignation triggers a contest to replace him as head of his party. The winner will become both party leader and prime minister, without the need for a national election.

Johnson had faced growing calls to go, after claims that he lied about the circumstances in which he gave a key role to an ally who was forced to quit last month over accusations that he had groped men.

Johnson's premiership has been embroiled in months of turmoil - last month he survived a vote of confidence among Conservative MPs - but the prime minister's undoing was ultimately prompted by the scandal surrounding one of their number.

Chris Pincher was appointed by Johnson as deputy chief whip, a senior role involved in maintaining discipline among fellow Conservative MPs. He resigned last weekend after being accused by two men of drunkenly groping them at a private members' club in London. Johnson had promoted Pincher in February to the position, which comes with pastoral care responsibilities for colleagues.

The prime minister declined to suspend Pincher from the party. Pressure began to build after four more allegations were reported in the Sunday papers, including accusations that he had groped two Conservative MPs. Pincher has denied the allegations.

Johnson apologised earlier this week after it emerged that he had been briefed that Pincher was the subject of previous sexual misconduct complaints before he appointed him. The prime minister said he had forgotten.