The Conservative MP Anna Soubry has apologised after saying Ukip leader Nigel Farage “looks like somebody has put their finger up his bottom”.

The comments were made on the BBC’s Andrew Marr show this morning, and while some viewers expressed their amusement on Twitter, others suggested “politics shouldn’t sink so low”.

The pair have a history of verbal clashes – last month after they both appeared on the BBC’s Question Time, the Ukip MEP said Ms Soubry was a “bully” who “attacked” him in a disagreement over immigration.

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Today she sat on the Andrew Marr sofa alongside Lord Mandelson and Vince Cable while the comedian Rory Bremner performed a series of impressions including David Cameron and Ed Miliband.

After Mr Farage had also been impersonated, Ms Soubry said: “I always think he looks like somebody has put their finger up his bottom and he really rather likes it.”

Though she was swiftly cut off by the show’s presenter Marr, the comment soon provoked a reaction on Twitter – not least from Mr Farage himself.

He tweeted to the Sun’s political editor Tom Newton Dunn, saying “Perhaps Anna Soubry should spend less time investigating digital rectal insertion and more on her brief?”

Mr Newton Dunn later wrote: “More from @Nigel_Farage on #fingergate: “She is rude and incompetent. I would expect an apology - but I won’t be holding my breath”.

The writer Caitlin Moran joked about the exchange, saying: “Please let Nigel Farage refute Anna Soubry's accusation with a press conference where he holds up his finger, as proof.”

Yet it was taken rather more seriously by the Labour MP Barry Sheerman, who said: “The Anna Soubry comment on Nigel Farage plumbs new depths in political debate and [David] Cameron should sack her now.”

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Ukip supporter David Jones, meanwhile, tweeted that the personal comments showed how: “Tories [are] seriously worried by UKIP threat.”

“Whatever you think of Anna Soubry or Nigel Farage, Soubry's comments on #marr are deeply unacceptable,” wrote the campaigner and blogger Jon Worth. “UK politics shouldn't sink so low.”

In a statement, Mr 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."

Ms 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.