Defence Secretary Sir Michael Fallon has apologised for putting his hand on a female journalist's knee.
The incident involved Julia Hartley-Brewer, who said she does not regard it as "anything other but mildly amusing".
A spokesman for Sir Michael said: "He had apologised when the incident happened 15 years ago and both Julia and he now considered the matter closed."
A friend of Sir Michael said: "Julia's a good friend of Michael's. He overstepped the mark when he put his hand on her knee. She made it clear it was unwelcome and he rightly apologised 15 years ago."
Ms Hartley-Brewer tweeted: "I have spoken previously about a Cabinet Minister who repeatedly put his hand on my knee during a party conference dinner.
"I calmly and politely explained to him that if he did it again I would 'punch him in the face'. He withdrew his hand and that was the end of the matter.
"I have had no issues since with the man in question and do not regard the incident as anything but mildly amusing."
Commenting on the Sun's front page, Ms Hartley-Brewer tweeted: "This "incident" happened in 2002. No one was remotely upset or distressed by it. My knees remain intact."
The revelation came as Parliamentary authorities are drawing up plans to allow victims of sexual harassment to report incidents "without fear", with abuse allegations continuing to dominate Westminster.
Commons Speaker John Bercow met with senior parliamentary figures on the House of Commons Commission to plot a way forward as fresh claims of sexually intimidating behaviour emerged.
In the latest of a slew of allegations about MPs' misconduct, the Daily Telegraph reported that a minister's "inappropriate" actions forced two female staff members to move to other jobs.
A spokesman for Commons Speaker John Bercow, who chaired the Commission meeting, said: "The Commission discussed the recent allegations relating to the harassment of staff, following today's exchanges in the House of Commons.
"It recognised that the current processes for dealing with this required review and a more thorough understanding of how they are put into practice by political parties.
"The Commission therefore committed to urgent work, in concert with the key stakeholders, to identify a way forward which would command general confidence and enable people to speak up without fear or favour."
Earlier, Leader of the Commons, Andrea Leadsom, told MPs that ministers would be sacked for inappropriate behaviour, saying: "If people are made to feel uncomfortable, that is not correct.
"In terms of the consequences for the perpetrators, I think I've also been perfectly clear that in the case of staff they could forfeit their jobs, in the case of Members of Parliament they could have the whip withdrawn and they could be fired from ministerial office."
In a statement to MPs, Mr Bercow called for change in Parliament amid what he described as "disturbing" allegations about a "culture of sexual harassment".
Mrs Leadsom is pressing the case for the establishment of a new external, specially trained support team to offer confidential advice and support to anyone suffering from sexual harassment at Westminster.
The move came as a Cabinet Office investigation got under way into alleged misconduct by international trade minister Mark Garnier, who is reported to have asked his Commons secretary to buy sex toys and called her "sugar tits".
Mrs May's official spokesman earlier declined to confirm that the Prime Minister has full confidence in Mr Garnier, saying he did not want to pre-empt the outcome of the inquiry.
The Wyre Forest MP has insisted that the incidents did not amount to harassment, describing the purchase of the vibrators as an instance of "high jinks".