A furious row has erupted at the heart of Ukip after its only MP and a millionaire donor clashed in a corridor at the party's annual conference.

Douglas Carswell accused Arron Banks of acting in an undemocratic manner by briefing journalists that he would be de-selected as the MP for Clacton unless he joined the businessman's campaign to leave the European Union.

Mr Banks called the incident a "hissy fit in a corridor" and refused to give Mr Carswell his backing.

But the MP insisted he had simply "politely and respectfully" asked the donor why he was threatening to oust him from the Commons.

The confrontation overshadowed Ukip leader Nigel Farage's keynote speech at the conference in Doncaster where he told activists that the new Leave EU umbrella campaign, led by Mr Banks, would unite eurosceptics.

Asked about the altercation, Mr Carswell told the Press Association: "Arron has announced that he's trying to build a cross party campaign to campaign to leave.

"I think it's a little bit unusual to go about that by suggesting that Ukip MPs who don't join it should be deselected and I merely, very politely, asked him why he was briefing journalists that unless I supported his campaign I would be deselected.

"It's not very democratic and it's a slightly unusual tactic to deploy in a run-up to a referendum.

"I very politely and respectfully asked him why he was going about that."

He added: "I never picked a fight with anyone.

"People have chosen to brief against me and suggest I would be removed from Ukip unless I did what they said.

"With great respect, it's the voters who decide who is and who isn't a Ukip MP.

"I'm not really sure that it's for Mr Banks to decide who is and who isn't a member of Ukip."

The row has broken out as Mr Carswell is currently a central part of a separate eurosceptic group, Business For Britain (BfB).

He insisted he had not been contacted by Mr Banks about joining the donor's faction and suggested that BfB had a better chance of winning the campaign to leave the EU.

"We're here overlooking a racecourse," Mr Carswell said.

"I'm not a gambling man but if I was I would probably bet on form.

"Now I can't help noticing that (senior BfB figures) Matt Elliott and Dominic Cummings have both been involved in two referendums where the establishment took one view and they took the other view and they won - one was on AV and one was on the North West referendum.

"If I was looking at a two horse race between these two campaigns to take the matter further I wouldn't want to put all my chips on one horse and not the other."

The former Tory said there was "absolutely no question of me being Ukip's MP in Parliament not being part of that cross-party group (BfB)".

He insisted he had briefed Mr Farage at every opportunity that he was part of BfB and that it was Ukip party policy to work with whichever campaign receives official designation from the Electoral Commission to fight one side in the referendum, and the money that comes with it.