Sources close to Defence Secretary Sir Michael Fallon have confirmed he was once rebuked by a journalist for putting his hand on her knee during dinner.
Radio presenter Julia Hartley-Brewer had recounted the “mildy amusing” incident without naming Sir Michael.
After his identity was revealed in The Sun, she tweeted saying she had not been “remotely upset or distressed”.
A spokesman for Sir Michael said he had apologised when it happened in 2002.
Ms Hartley Brewer, who has criticised “wild rumours and claims” circulating at Westminster, said she did not consider herself a victim after the incident over dinner at the Conservative Party conference.
After the minister kept putting his hand on her knee, she said: “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.”
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.”
It comes amid allegations about sexual harassment at Westminster.
The government has promised urgent action to improve the way complaints about the way MPs’ staff are treated are handled.
On Monday Commons Leader Andrea Leadsom said recent allegations against MPs “risked bringing all our offices into disrepute”.
Commons Speaker John Bercow said there must be “zero tolerance” of sexual harassment in Parliament.