Ukip is being run by a bunch of "circus clowns", the party's leading financial backer, Arron Banks, has claimed.
And as Ukip plunged deeper into bitter in-fighting following the shock resignation of leader Diane James after just 18 days in the post, one of the candidates to take her place, Raheem Kassam, branded the party riddled with "corruption".
Mr Banks called on Ukip's sole MP, Douglas Carswell, to be thrown out as the major donor turned his fire on party's ruling national executive committee (NEC).
"This body is populated by a motley collection of amateurs; leftovers from a bygone age, when Ukip was a ragtag band of volunteers on the fringes of British politics. Watching them try to run the modern political movement that (Nigel) Farage built is like watching a team of circus clowns trying to carry out a pit stop at the Silverstone Grand Prix.
"If James hadn't put her name forward at the last minute, we would have had nothing but a rabble of no-name, no-talent nobodies to choose from. These people would be out of their depth in a paddling pool, and couldn't be more unfit to run a modern political party," Mr Banks wrote in the Guardian.
The attack came as Mr Kassam insisted the party was beset by back-stabbing and duplicity.
"I, like ordinary Ukip members, am so tired of the games that are being played at the top of this party. There is so much corruption. There is so much duplicity. There are so many people shaking hands with one another and then knifing them in private. It has to stop," he said.
With the party reeling from Ms James's surprise decision to quit, the favourite to replace her, MEP Steven Woolfe, admitted he had flirted with defecting to the Tories after being barred from the last leadership race by the party's NEC.
Mr Woolfe said he had been "enthused" by Theresa May's start to her premiership but in the end concluded that only Ukip could be relied upon to deliver on Brexit.
"Her support of new grammar schools, her words on social mobility and the growing evidence that she is committed to a clean Brexit prompted me, as it did many of my friends and colleagues, to wonder whether our future was within her new Conservative Party," he said.
"However, having watched the Prime Minister's speech on Sunday, I came to the conclusion that only a strong Ukip can guarantee Brexit is delivered in full and only our party can stand up for the communities of the Midlands and the North."
Ukip's NEC will now meet on October 17 to agree a timetable for an election to find a permanent replacement for Ms James.
In her resignation statement, Ms James she said she was standing down for "personal and professional" reasons, citing a lack of support among the party's MEPs and officials.
It is thought that her husband's ill-health may also have played a role, while Nigel Farage, who will head the party until a replacement is elected, pointed to an incident at London's Waterloo station in which she was verbally abused and spat at.
Mr Farage said he expects a new leader to be appointed before the end of November.
Former deputy leader Paul Nuttall, former deputy chairwoman Suzanne Evans, who has just returned to Ukip after a suspension, and Lisa Duffy, who came second to Ms James in the last leadership contest, are all said to be considering a leadership bid.
The back-biting came as Mr Farage accused the Conservatives of rebranding as Ukip after Mrs May's keynote address to the Tory Party conference.
"It made you realise the extent to which Ukip hadn't just pushed for, gained and helped to win a referendum, but actually we've changed the centre of gravity of British politics.
"Virtually everything she said in that speech are things I've said to the Ukip conference over the last five or six years," Mr Farage told Channel 4 News.