Damian Green, the effective deputy prime minister, has resigned after he was found to have made "inaccurate and misleading" claims regarding historical allegations that he had pornography on his work computer.
Theresa May said she was "extremely sad" but had no choice but to request Green's resignation after a Cabinet Office inquiry concluded he had broken the ministerial code.
Green, who served as first secretary of state and minister for the Cabinet Office, had been accused of inappropriate behaviour by Conservative activist Kate Maltby.
Following those allegations, a former police officer went public with claims that porn had been found on Green's parliamentary computer during an entirely separate 2008 investigation.
A Cabinet Office inquiry concluded that while Green had "generally been both professional and proper", he broke the ministerial code by publicly denying he knew of allegations porn had been found on his work computer in 2008. In reality the police had informed his lawyers at the time and raised the issue with him again in 2013.
The investigation did not reach a conclusive verdict on whether he had acted inappropriately with Maltby, a Tory activist who was also an old family friend. However, despite "competing and contradictory accounts", it concluded her account of inappropriate touching was "plausible".
Green used his resignation letter to maintain that he did not download or view pornography on parliamentary computers but admitted he had not handled the issue well: "I accept that I should have been clear in my press statements that police lawyers talked to my lawyers in 2008 about the pornography on the computers, and that the police raised it with me in a subsequent phone call in 2013. I apologise that my statements were misleading on this point.
"The unfounded and deeply hurtful allegations that were being levelled at me were distressing both to me and my family and it is right that these are being investigated by the Metropolitan police’s professional standards department."
He also apologised to Maltby, who made the allegations against him in a piece for the Times newspaper.
"I deeply regret the distress caused to Kate Maltby following her article about me and the reaction to it. I did not recognise the events she described in her article, but I clearly made her feel uncomfortable and for this I apologise."
Kate Maltby declined to comment pending the release of the full report from the Cabinet Office. Instead her parents, formerly close friends of Green, issued a statement in support of her decision to speak out: "We are pleased that the Cabinet Office has concluded its enquiry into the conduct of Damian Green. We are not surprised to find that the inquiry found Mr Green to have been untruthful as a minister, nor that they found our daughter to be a plausible witness.
“We have received many supportive messages from people near and far who appreciate Kate’s courage and the importance of speaking out about the abuse of authority. We join with them in admiring her fortitude and serenity throughout the length of the investigation and despite the attempted campaign in certain sections of the media to denigrate and intimidate her and other witnesses. We are proud of her.
"We have ourselves known of these incidents since they first occurred and have fully supported Kate in the responsible manner in which she has reported them."
Green is the third cabinet minister to have been forced out in the last two months, following Michael Fallon and Priti Patel.