Sky News understands that Boris Johnson’s deputy chief has resigned over a “deception” complaint.
Chris Pincher said he had drunk “too much” and had “embarrassed myself and others” on a night out.
“I apologize to you and those concerned,” he added.
Labor Deputy Leader Angela Rayner said the prime minister had “serious questions to answer” about why Mr Pincher had “been given that role in the first place and how he could remain a Conservative MP”.
His departure comes less than a week after former Conservative President Oliver Dowden resigned due to two partial election defeats.
This is the second time Mr. Pincher has left the whips office.
In November 2017, Downing Street said it had “voluntarily referred to both the party’s grievance procedure and the police.”
The Mail on Sunday reported that Mr Pincher had been accused of making an unwanted pass to conservative activist and former British rower Alex Story.
Pincher told the newspaper, “If you’ve ever been offended by Mr. Story for something I said, I can only apologize.”
Tamworth’s Conservative MP wrote to Mr Johnson explaining his decision to resign.
He said in his letter, “Last night I drank too much.
“I have embarrassed myself and other people, which is the last thing I want to do and for that I apologize to you and to those concerned.
“I think what needs to be done in these circumstances is for him to resign as deputy director.
“I owe it to you and the people I’ve caused anguish to do this.”
Mr Pincher added: “I want to assure you that you will continue to count on my full support from subsequent banks, and I wish you all the best to meet the COVID aftershocks and the challenges of international inflation.
“It has been the honor of my life to have served in Her Majesty’s government.”
Ms Rayner said the resignation showed “the extent to which standards of public life have been degraded under the control of Boris Johnson”.
He added: “The Conservative Party is so immersed in scandal and scandal that it is totally unable to meet the challenges facing the British people.”
Johnson has been fined by metropolitan police for violating the blocking rules.
Image: MP Pincher has been a Member of Parliament since 2010
Chris Pincher has been a Member of Parliament since the 2010 general election, when the Conservatives formed a coalition with the Liberal Democrats.
Prior to becoming deputy director of the team he was Minister of State for Europe and America and Minister of State for Housing.
He also writes a column on alcoholic beverages for The Critic magazine. One recently titled, “Falling into the Gin Trap.”
The Conservatives are not the only party currently suffering from poor quality allegations.
Earlier this month, it emerged that SNP MP Patrick Grady was facing suspension from the House of Commons after an allegation of sexual misconduct was confirmed following a parliamentary inquiry.
A group of independent experts recommended Mr Grady be suspended from the House for two days for making an “unwanted sexual breakthrough” to a party staff member at a social work event at a pub in 2016.
Mr. Grady was also ordered to apologize publicly in the courtroom and to apologize privately to the person who complained.
The leader of the SNP in Westminster, Ian Blackford, has faced calls to resign in connection with the same matter.