One of UKIP's biggest donors has said Douglas Carswell, the party's only MP, is "borderline autistic with mental illness wrapped in".
Arron Banks, who has given £1 million to UKIP, made the comment in response to a question from BuzzFeed News about why Carswell had announced he would support the Business for Britain campaign as the best route to leave the EU rather than Banks's own Leave.EU campaign, which is endorsed by UKIP.
In response, Douglas Carswell told BuzzFeed News: "I think it's best if I decline to comment. I think the comments are best not dignified with a response."
Asked whether he was comfortable with the role Banks was playing in UKIP, Carswell said: "It's not really up to me to decide those things and I'd prefer not to comment on what Mr Banks has said."
The two men had clashed earlier in the day in full view of journalists in the press room at UKIP's annual conference in Doncaster. The argument came after Banks suggested to the Guardian that Carswell should face deselection if he failed to back Leave.EU, which has the support of Nigel Farage and the party establishment.
UKIP press officers were seen desperately searching for a copy of the newspaper, which Carswell then sat reading in a corner of the press room.
The clash occurred because Carswell has chosen to back Business for Britain, a Eurosceptic group run by veteran campaigner Matthew Elliot, because he believes it has a greater chance than Banks' group of leading Britain out of the EU in the forthcoming referendum.
Shortly before Banks made the comments, Nigel Farage had insisted UKIP was separate from Leave.EU at a press briefing for journalists.
The UKIP leader suggested Carswell was only backing the rival campaign because of his history as a Tory MP: "Douglas may have a residual loyalty to his old friends in the Conservative party."
Farage went on to insist that UKIP was a separate entity to Banks' campaign. Minutes later Banks wandered into Farage's private press briefing and began answering questions.
Listen to Banks' comment here:
This is the full conversation:
BuzzFeed News: "Douglas Carswell has just issued a statement saying that today's events more than ever have convinced him that the group to get official designation is the one headed by Business for Britain..."
Arron Banks: "[laughs] He's borderline autistic with mental illness wrapped in..."
Aides: "Say it's off the record, say it's off the record..."
Update: Banks has since apologised for the comments but maintains Carswell was "appalling rude" towards him.
In a statement he said: "Douglas Carswell was appalling rude and provocative towards me today. Which does not justify my comments for which I apologise."