Defence Minister Anna Soubry has apologised after saying Ukip leader Nigel Farage "looks like somebody has put their finger up his bottom".
The Tory clearly surprised fellow guests on BBC One's Andrew Marr Show when she made the remarks following an impression of Farage by comedian Rory Bremner.
Farage later said he was "astonished" by the "foul-mouthed attack" and insisted the minister had "stooped to the levels of crudity that any politician would spend a lifetime apologising for".
During a light-hearted discussion at the end of the show, a chuckling Soubry made a gesture with her finger and said: "I always think he looks like somebody has put their finger up his bottom and he really rather likes it."
Bremner said: "Are you allowed to say that?"
Lord Mandelson, who was also on the sofa, grabbed her arm, and said: "Anna, Anna, please, it's too early."
In a statement, Farage said: "This is a woman who was proven to not even have a grip on her portfolio back in November when on Question Time she showed she had absolutely no idea about the Royal Navy support ships being built in South Korea.
"She also launched a vile attack on me then, claiming I was 'putting fear into people's hearts' by raising concerns over unrestricted immigration. The same concerns that today her party are so desperate to try to address.
"But this latest, remarkable foul-mouthed attack is utterly incredulous. Soubry has stooped to the levels of crudity that any politician would spend a lifetime apologising for.
"This is supposed to be a professional woman representing her political party on a national television programme on a Sunday morning. Well, I am astonished, and I would imagine the rest of her party is too, as well as deeply embarrassed."
Soubry said: "If he is in any way offended, I apologise unreservedly. It was a light-hearted remark."
A No 10 source said the minister had apologised and they had nothing further to add.