Key Ukip donor Arron Banks has deepened the party’s bitter split with an extraordinary threat to stand against its only MP.

Mr Banks revealed he intends to try to unseat Douglas Carswell, the former Conservative MP who retained his seat in Clacton, Essex, for Ukip at the last general election.

His aide confirmed that the donor had already arranged an office in order to mount the challenge in 2020.

The move comes after Mr Banks threatened to pull his huge funding for Ukip unless he is made chairman so he can “purge” members and stop it being “run like a jumble sale”.

Meanwhile, Nigel Farage – his close ally – called for Mr Carswell to be thrown out of the party, after a feud apparently motivated by anger at the MP’s failure to secure him a knighthood.

At the weekend, Mr Banks blamed “dullards” such as Mr Carswell for not bringing in enough Tory votes, following Ukip’s defeat to Labour in last week’s Stoke-on-Trent Central by-election.

Defeat was the “final straw” for Mr Carswell, whom he accused of being preoccupied with “sabotaging” a knighthood for former leader Nigel Farage, an allegation strongly denied by the MP.

Mr Banks told The Sunday Express: “If [party leader Paul] Nuttall doesn't professionalise it and toss out the likes of Douglas Carswell, Suzanne Evans and the rest of the Tory cabal then the party is finished anyway.

“These dullards aren’t bringing in Tory votes, so what are they for? The party now needs to bring in serious people.

“From what I hear, Carswell’s main concern is sabotaging Nigel’s knighthood, which is why he must leave the party.”

The assault came as Nigel Farage called for Mr Carswell to be thrown out of the party because he is actively attempting to damage it.

His colleague had “sought to split and divide Ukip in every way imaginable” since he defected from the Conservatives in 2014 and became Ukip’s first MP, the former leader alleged.

Mr Farage wrote, in The Daily Telegraph: “I think there is little future for Ukip with him staying inside this party. The time for him to go is now.”

However, Mr Farage’s blast appeared to have been triggered by fury at the former leader’s failure to secure a knighthood.

Ukip’s former leader, Lord Pearson of Rannoch, tried to organise a peerage for Mr Farage but lobbied instead for a knighthood when it became apparent he would have had to quit as an MEP.

After the bid was rejected he asked Mr Carswell to approach Government chief whip Gavin Williamson to appeal the decision.

On 31 December, the Ukip MP wrote in an email to the peer: “As promised, I did speak to the Government chief whip.

“Perhaps we might try angling to get Nigel an OBE next time round? For services to headline writers? An MBE, maybe? Let’s discuss...”