A senior Ukip MEP has quit, complaining there is no-one good enough to lead the party after incumbent Henry Bolton's affair with Jo Marney, which ended after racist comments she made about Meghan Markle were exposed.
Ukip Treasury spokesman Jonathan Arnott said he had "forlorn hope" when Mr Bolton was elected leader in September but it has become "abundantly clear" he is not the right person for the job.
"But likewise that those jockeying for position and hoping to take his job would be no better," he added in a statement on his website.
Mr Bolton, 54, was forced to end his relationship with the 25-year-old model after the publication of text messages in which she made disparaging comments about Prince Harry's fiancee Ms Markle.
He is expected to face a vote of no confidence at an emergency meeting of Ukip's National Executive Committee in London on Sunday, called to discuss the controversy over his leadership.
Mr Bolton announced on Monday that the "romantic side" of his relationship with Ms Marney was over following the exposure of text messages in which she called Ms Markle a "dumb little commoner" whose mixed-race background would "taint" the royal family.
The Mail on Sunday printed texts it said had been sent by Ms Marney, including use of the word "Negro" and a message reading "This is Britain, not Africa" during a discussion about the royal engagement.
Mr Bolton was on Wednesday photographed with his former girlfriend in the bar of a London gentlemen's club and later in the evening at the railway station in Folkestone, where he lives.
An aide told the Press Association that Mr Bolton had explained that his former partner went back with him to pick up some bags before returning that evening to her home in Maidstone.
Mr Bolton later released a photograph of a local taxi company's log to show that a cab had picked someone up from the address to go to the station.
Mr Arnott said the fiasco was the final straw after a tumultuous 18 months for the party.
"The unpleasant nature - the Steven Woolfe fracas, the Diane James fiasco, the Anne-Marie Waters debacle, the John-Rees Evans bizarreness, the countless leaks, briefings and character assassinations - became almost as bad as the political establishment I had hoped to counter," he said.
"With yet another new leader came new forlorn hope. Over the last week it has become abundantly clear that the current leader is not the right person for the job, but likewise that those jockeying for position and hoping to take his job would be no better. Politics has always been like that, but as true believers in a cause, we always thought ourselves to be different. Once, maybe, but no longer."