Boris Johnson is facing calls to suspend his former deputy chief whip as a Tory MP, after allegations he groped two men at a private members' club.
Chris Pincher quit his government post on Thursday, saying in a resignation letter he "drank far too much" and "embarrassed myself and other people".
Labour's Yvette Cooper called for his suspension whilst the "really serious" allegations are formally investigated.
"This is about sexual assault," she added.
The BBC has approached Mr Pincher, the Conservative Party and the Tory whips' office for comment.
Downing Street suggested the prime minister considered the matter closed.
A No 10 spokesperson said they were "not aware of any sort of government investigation", and that Mr Johnson was not aware of any specific allegations against Mr Pincher before he appointed him as deputy chief whip in February.
In a letter to the chief whip, Chris Heaton-Harris, two senior female Tory MPs said the party's recent approach to allegations of sexual misconduct posed a risk of "serious reputational damage".
Caroline Nokes and Karen Bradley said anyone under investigation for such allegations should not be allowed to represent the party and called for a new code of conduct for Tory MPs.
The Sun newspaper first reported Mr Pincher's resignation, saying he was drinking at the Carlton Club in central London when he is said to have assaulted two other male guests.
Several concerned Tory MPs contacted the Conservative whips' office to complain about his behaviour, the paper said.
Dozens of people were present in a small room with a bar at the private members' club including other MPs, ministers, club officials and people working in public relations, the BBC understands.
In a resignation letter on Thursday, Mr Pincher wrote to the prime minister: "Last night I drank far too much."
He added: "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."
On Thursday, a Downing Street source said as things stood Mr Pincher would face no further action from the party and would keep the whip, allowing him to continue to sit as a Conservative MP.
A Tory MP told the BBC they had raised concerns about Mr Pincher's behaviour to senior figures in Number 10 and the Conservative Party - including chief whip Chris Heaton-Harris, minister Nigel Adams, government whips and one of the prime minister's top advisers Ben Gascoigne.
Speaking about raising concerns, the MP said: "Loads [of us] did when he was in the frame for chief whip and he never got it. There were concerns, none of us had proof we could use. He should have the whip suspended and a by-election."
Former Tory MP Neil Parish told the BBC Mr Pincher should be suspended by the party, as he was in April was after he admitted to watching pornography in Parliament.
Mr Parish subsequently stood down as an MP, triggering a by-election in his constituency of Tiverton and Honiton.
"I believe it to be total double standards," Ms Parish said. "The whip should be suspended immediately from Christopher Pincher and then he can refer himself to the standards board, and it can be all investigated and he can resign."
Shadow home secretary Ms Cooper told BBC Radio 4's Today programme: "This is just a total disgrace, the response from Boris Johnson, from the government to this.
"These allegations are really serious, this is about sexual assault.
"So the idea that the response that we've seen - that the prime minister thinks he's done the decent thing by resigning, that there's no need for an investigation - that's a total disgrace."
Liberal Democrat chief whip Wendy Chamberlain said: "Given the seriousness of these allegations, it's difficult to see how Chris Pincher can continue as an MP.
"There now needs to be a full investigation and in the meantime Chris Pincher should have the Conservative whip withdrawn."
Tensions are bubbling in the Tory party about Number 10's line that Christopher Pincher has recognised his wrongdoing and therefore no further action should be taken.
Multiple Tory MPs, and some ministers, on the contrary think he needs to lose the party whip - meaning he would no longer sit as a Conservative MP.
One tells me they personally raised concerns about Mr Pincher's behaviour in the past, and they added "loads of us" raised concerns back when some thought he would be made the party's chief whip, but ended up being made deputy.
Multiple government ministers have also told the BBC that "of course" he should not keep the whip - despite what No10 are pushing.
It's telling, too, listening to how the cabinet minister brought out to defend the government line, Simon Hart, answered when asked if Mr Pincher should lose the whip.
He told Sky News: "I know what I'd like to see happen. You can probably tell what that is just from the way I'm trying to avoid answering your question", and said that the chief whip would be looking into this.
As ever, pressure from within government could continue to mount on No10 if ministers feel they are being made to defend something that some of them, quite obviously, don't want to.
Asked whether Mr Pincher was being formally investigated, Mr Hart warned against rushing any probe, saying it could be "counter-productive".
He added that the chief whip would treat the matter "with the utmost seriousness" and should be afforded "the space to properly assess the situation" with others.
"It is absolutely proper that they spend today going through this with a fine tooth comb," he told the Today programme.
Mr Pincher previously stood down from the whips' office in 2017, when he was accused of making an unwanted pass at former Olympic rower and Conservative activist Alex Story.
But after an investigation by the party, he was cleared of any breach of its code of conduct.
Mr Pincher was first elected as MP for Tamworth in 2010 and served as a minister under former Prime Minister Theresa May.
He has served in the whips' office in Mr Johnson's government since February 2022, and was previously a minister in the Foreign Office and the Levelling Up Department.
Whips are MPs who are in charge of party discipline, and who have the job of trying to ensure that all MPs on their side vote with the party line in Parliament.
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