Damian Green, one of Theresa May’s closest allies, has been sacked from the cabinet after an inquiry found he had breached the ministerial code.
He was “asked for quit” after he was found to have made “inaccurate and misleading” statements about what he knew about claims pornography was found on a computer in his office in 2008.
In his resignation letter, Mr Green apologised for his actions.
BBC’s Laura Kuennsberg said the PM “had little choice but to ask him to go”.
In her written response, Mrs May expressed “deep regret” at his departure.
Mr Green, who as first secretary of state was the PM’s deputy, had been under investigation regarding allegations of inappropriate conduct.
He denied suggestions that he made unwanted advances to a female journalist, Kate Maltby, in 2015 and viewed pornography on a computer in his Commons office in 2008.
Damian Green quits cabinet over cover-up of office porn
Deputy PM lied about knowledge of material
Theresa May forced Damian Green, her deputy and closest ally, to resign tonight after he admitted making “inaccurate and misleading” statements about pornography found on his parliamentary computer.
In the biggest resignation of the Westminster sex scandal, Mr Green was found to have lied when he denied knowledge of indecent material found on his Commons computer by police in 2008.
A Cabinet Office inquiry also concluded that allegations of inappropriate behaviour towards Kate Maltby, a Tory activist and journalist 30 years his junior, were “plausible”.
In a letter to Mr Green released by Downing Street at 9pm on the last day before parliamentary recess, Mrs May said it was with “deep regret” that she had asked him to step down but his conduct fell short of the “high standards” the public demanded. She rounded on former police for divulging the contents of Mr Green’s computer, which were uncovered during a leaks inquiry but remained secret for nine years.