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Police have confirmed they are investigating after Nigel Farage vowed to "take the knife to the pen pushers in Whitehall" during a Brexit Party rally in Wales.

Farage was addressing the 500-strong crowd in Newport last week when he made the comments.

He told the audience: "Once Brexit is done, we will take the knife to the pen pushers in Whitehall."

Alliance Party MEP Naomi Long asked police on Twitter if they would be investigating "this clear case of incitement to violence against staff in the civil service".

Gwent Police replied, saying: "We have been made aware of comments made last night in Newport and we are looking into these allegations."

Since news of the police investigation became public, Farage has addressed the controversy by tweeting: "I should have said 'take the axe', which is a more traditional term for cuts."

(Image: Avalon.red)

The rally is part of a nationwide conference tour in which Nigel Farage will address audiences around the country

The comments come amid growing concern about the language used by politicians in the Brexit debate. Yesterday, former Home Secretary Amber Rudd accused Boris Johnson of "inciting violence" for using words like "Surrender Act", "traitor" and accusing MPs of "betraying" the people.

Johnson was also under fire this week after he rubbished concerns raised by Labour MP Paula Sherriff about his "inflammatory" language.

Sheriff told the Commons she receives death threats every day, and warned Johnson that many threats "quote his words". However, the prime minister replied he had "never heard such humbug in all my life."

He has also refused to apologise for saying that delivering Brexit was the best way to "honour the memory" of murdered MP Jo Cox.

(Image: Getty Images) (Image: Avalon.red) (Image: Getty Images)

Earlier this week Farage tweeted his support of Johnson, saying he is "right" to use words like surrender and betrayal.

Farage has faced fury over his language before. Last month he reportedly told the Conservative Political Action Conference in Sydney, Australia, that Prince Harry had "fallen off a cliff" since meeting Meghan Markle, in a speech that was accused of being "laced with barely concealed racism" by Labour MP Stephen Doughty.

Fellow Brexit Party member and MEP Ann Widdecombe caused uproar in July when she compared Brexiteers to slaves rising up against their owners .

Earlier this year Nigel Farage demanded police take action over a joke made by comedian Jo Brand about throwing battery acid at him. He said Brand was "inciting violence" with the joke.

The South Wales Argus reported that Farage boasted of putting "fear in the hearts of the MPs in Wales" at the rally. He described the Speaker John Bercow as a "ghastly little man" and the prime minister of Luxembourg Xaviel Bettel as a "perfectly vile little pipsqueak".