Theresa May asked Damian Green to stand down after he was found to have misled the public over a pornography scandal.
A formal investigation found that Green misled the public by claiming he was never told about pornography found by police on his parliamentary computer.
Green was effectively deputy prime minister until he quit on Wednesday night.
He is the third cabinet minister to resign in three months, following Defence Secretary Michael Fallon and International Development Secretary Priti Patel.
LONDON — Damian Green has resigned as First Secretary of State after an investigation found he misled both Parliament and the public over claims that he watched pornography on his parliamentary computer.
A formal investigation by the government found that Green made misleading public statements about pornography found on his Westminster office computer by police in 2008.
He is the third minister to resign from Theresa May's cabinet in less than two months.
A seven-week investigation concluded that both he and his solicitor did know about explicit material that was found on his computer nine years ago.
This is at odds with public statements he made, in which he flatly denied that he had been told there was pornography on the computer, and described claims to the contrary by a former police officer as "false, disreputable political smears".
Green, the MP for Ashford, offered his resignation to May after by letter after she told him he had no option but to stand down.
As First Secretary of State, Green was effectively Theresa May's deputy. The two met have been friends and political allies for decades. They first met while studying at Oxford University, joined parliament at the same election and were both ministers in the Home Office during David Cameron's tenure as Prime Minister.
Green's resignation is the latest in a series of blows to Theresa May, who had already lost two cabinet ministers since the general election in May.
Her Defence Secretary, Michael Fallon, resigned over harassment allegations in early November, and the International Development Secretary, Priti Patel, left a week later after failing to declare meetings with the Israeli government.
(Photo by Daniel Leal-Olivas - WPA Pool /Getty Images)
The Cabinet Office investigation into Green did not make a judgement on whether he watched pornography on his parliamentary computer, the central allegation against him.
But it found that his handling of the allegations was enough to breach ministerial rules.
It investigation also considered claims made by Conservative activist Kate Maltby that Green touched her knee at a pub in Waterloo in 2015. It stopped short of saying whether or not it happened, but described her account as "plausible."
In his letter to Prime Minister May, Green wrote:
"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.
"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."
In her response, May cited the report's conclusion that Green made misleading public statements regarding pornography claims on 4 and 11 November, and that his behaviour had been in breach of the Ministerial Code.
"This falls short of the seven principles of public life and is a breach of the ministerial code – a conclusion which has been endorsed by Sir Alex Allan, the independent adviser on ministers’ interests.
"While I can understand the considerable distress caused to you by some of the allegations which have been made in recent weeks, I know that you share my commitment to maintaining the high standards which the public demands of ministers of the crown.
"It is therefore with deep regret, and enduring gratitude for the contribution you have made over many years, that I asked you to resign from the government and have accepted your resignation."
Maltby is yet to respond to Green's resignation, however, her parents Colin and Victoria said they were "not surprised" that Mr Green had been found to have misled people.
May was given the findings of the Cabinet Office investigation on Monday and passed it on to Alex Allan, her independent adviser on ministerial standards, who agreed with its conclusions, according to a report by The Daily Telegraph.
Here is Green's letter to Theresa May:
And her response to him:
10 Downing Street