Keir Starmer says the Conservatives must take immediate action against the MP who watched porn in the Commons, instead of leaving it an independent investigation.
The Tories have referred the controversy to the Independent Complaints and Grievance Scheme (IGS) – promising “appropriate action” if the allegation is proved.
But the Labour leader said there is no need for the party to await the inquiry’s conclusions, because the MPs’ identity is known to its whips’ office.
“This is an unusual case because the Tory Party knows who this individual is,” he said, on the local elections campaign trail in Cumbria.
“I think that they should deal with it and deal with it sooner rather than later and take appropriate action.
“So, nothing wrong with the independent process, but I think the Tory Party, they know who this is, they should take action now.”
The criticism came as Boris Johnson’s official spokesman said he did not know which MP is being accused and referred inquiries to the Conservative Party.
Although an ICGS inquiry requires a complaint to be made by someone who witnessed an alleged incident, this is not believed to be an obstacle to it taking place.
Allegations of sexism and misogyny have engulfed the Tories, after a male Conservative MP was accused by two female colleagues of openly watching pornography on his phone.
One of the MPs, a minister, said the incident took place in the chamber last week and separately during a committee hearing, telling colleagues the man was aware he had been seen, yet continued watching.
A second female Tory MP said she had also seen the man watching pornography. She is believed to have she had attempted to film him as proof of what he was doing.
Government sources have suggested the man in question is a backbencher – not a minister – implying his identity is known.
The prime minister said on Wednesday that he considered sexual harassment “intolerable” and agreed that it should be “grounds for dismissal”.
However, a spokesperson for the chief whip said, late on Wednesday: “Following allegations of inappropriate behaviour in the House of Commons the chief whip has asked that this matter be referred to the ICGS.
“Upon the conclusion of any ICGS investigation the chief whip will take appropriate action.”
The party has acknowledged that “only that people who have witnessed the situation” can make a complaint to the body – which means the party cannot.
The meeting at which the allegation emerged was attended by some of the most senior women in the Conservative Party, including Theresa May, and some current ministers.
The Independent has been told that the “united view of the meeting is that this MPs should be suspended by the party”.