Tory Defence Minister Anna Soubry joked on a BBC news show that Ukip leader Nigel Farage "looks like somebody has put their finger up his bottom and he really rather likes it."
Her surprising interjection came on the Andrew Marr show, where she sat with Lord Mandelson, the former Labour party advisor, and Business Secretary Vince Cable.
The trio were watching impressions of Ed Miliband and David Cameron by comedian Rory Bremner. But watching one of Nigel Farage, Soubry said: "I always think he looks like somebody has put their finger up his bottom and he really rather likes it."
He spoke later to the Sun's Political Editor Tom Newton Dunn:
Farage told the Express: "This latest, remarkable foul mouthed attack is utterly incredulous. Soubry has stooped to the levels of crudity that any politician would spend a life time 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, who has now apologised for her remark, has done battle with Farage before.
On Newsnight in November, she accused the Ukip leader of putting "fear in people’s hearts" and accused him of spreading prejudice. "Turn to the stranger and you blame them," she said.