Boris Johnson is facing an accusation that he lobbied to get a young woman a job at City Hall while they were having a sexual relationship.
The woman has claimed that Mr Johnson abused his power when he was London mayor to have a relationship with her.
The prime minister allegedly secured an interview for the young Tory activist in 2008 just weeks after meeting her and bringing her back to his parliamentary office, the Sunday Times has reported.
However, Cabinet Office minister Kit Malthouse turned her down for the role because he felt that she and Mr Johnson had become too close, the paper said.
It is said the woman wanted a meeting with Mr Johnson nine years later at the height of the #MeToo movement. She reportedly told him in the meeting that she felt uncomfortable about the relationship they had.
She recorded the conversation over fears she wouldn’t be believed and said she was “really shaken and upset” about what had happened in their short time together, the paper said.
The woman told Mr Johnson, who was by then foreign secretary, that it was an example of how any young woman who “steps into this building is fair game” and they were there to be “leered at” by powerful men.
In the recording Mr Johnson said he was “very disappointed” she didn’t secure the job and said one of the reasons given by Mr Malthouse was that “he thought you were too friendly with me”.
The paper said that Mr Johnson denied he did anything in an “abnormal” way to help her and said that you can’t just “machine friends into jobs” in City Hall.
Responding to the report, Liberal Democrat deputy leader Daisy Cooper said: “The woman’s account is deeply distressing to read and it’s clear this must be investigated immediately, either by a parliamentary body or city hall authorities.”
She added: “The public already know this man isn’t fit to be prime minister. For the good of the country, Boris Johnson must resign now. Above all else, this distressing report must be independently investigated.”
Labour’s deputy leader, Angela Rayner, said the allegations could be added to the “growing list of appalling and exploitative behaviour carried out by this Tory government”.
She added: “These awful allegations add to the lies, the law breaking and the security breaches – this man is not fit for office and should go now.”
Ms Rayner said Mr Malthouse “should also explain why he covered up for Boris Johnson and continued to back him all this time”.
A Downing Street spokesperson told the paper: “This not about his time as PM and no public interest as I see it. And we don’t talk about his private life.”
The Independent has contacted Downing Street for comment.