The former deputy chief whip at the centre of groping allegations has said he is seeking "professional medical support" and that he hopes to return to his duties as an MP "as soon as possible".
Chris Pincher, who was suspended from the Conservative Party on Friday night after Downing Street admitted that it was warned not to appoint him, said he would "cooperate fully" with an inquiry into his behaviour.
Mr Pincher had the whip removed following claims that he drunkenly groped two men at a private members club in London on Wednesday evening.
In a statement Mr Pincher said: "I respect the Prime Minister's decision to suspend the whip whilst an inquiry is underway, and I will cooperate fully with it.”
'I drank far too much, embarrassing myself and others'
He added: "As I told the Prime Minister, I drank far too much on Wednesday night, embarrassing myself and others and I am truly sorry for the upset I caused.
"The stresses of the last few days, coming on top of those over the last several months, have made me accept that I will benefit from professional medical support.
"I am in the process of seeking that now, and I hope to be able to return to my constituency duties as soon as possible."
It is the second time Mr Pincher, the Conservative MP for Tamworth, has quit the Tory Whips Office over allegations of sexual impropriety.
In his letter to Mr Johnson, Mr Pincher said he would be resigning and appeared to address the allegations.
He wrote: “Last night I drank far too much. I’ve embarrassed myself and other people, which is the last thing I want to do, and for that I apologise to you and to those concerned.
“I think the right thing to do in the circumstances is for me to resign as deputy chief whip. I owe it to you, and the people I’ve caused upset to, to do this.”
Lurid details have emerged of Mr Pincher’s conduct on the night in question, including claims he was so drunk he could “barely stand up” and that a fellow Tory MP had to “drag” him out of the exclusive private member’s bar.
The then deputy chief whip had attended a Conservative Friends of Cyprus event at the Carlton Club, at which prosecco and wine was served. He gave a short speech and witnesses said he was not drunk.
'He was far too drunk to be there'
But after the gathering broke up at 9pm and most colleagues left, he stayed behind and is said to have become more inebriated. It was later on that the 52-year-old is said to have groped the two men, one of whom is in his 20s.
One Tory MP who was present at the scene told The Telegraph how they “threw out” a “very drunk” Mr Pincher after being told about one of the two sexual assaults and then called the chief whip at 3am to inform him.
“I was made aware of the first situation, and I took him outside and told him to leave, because he was too drunk,” the MP said. “I was told he had been inappropriate with someone, and apparently he had run his hands down him.
“He was in and out of my periphery and I could see he was far too drunk to be there. Somebody else was trying to get him to leave and not being successful. That’s when I basically dragged him outside.”
Claims have also emerged from the Politico website that Mr Pincher had been given a government “minder” who accompanied him to events to make sure that he did not get too drunk.
In 2017, Mr Pincher quit a more junior position in the whip's office after being accused by a former Tory candidate of trying to chat him up.
Alex Story, an ex-Olympic rower, said he had invited him back to his flat and acted “like a pound shop Harvey Weinstein” untucking his shirt, massaging his neck and whispering: “You’ll go far in the Conservative Party.”
A former activist in the party’s youth wing said that Mr Pincher was known as “Uncle Monty” amongst young Tories - a reference to a predatory homosexual character in the cult film Withnail and I.