Ukip's founder, Professor Alan Sked, has issued a withering verdict of Douglas Carswell's leadership potential, saying he has "the charisma of a wet turd".
Sked, who was the party's first leader, told the Huffington Post UK that the Clacton MP "might offer a focus for opposition" to Nigel Farage within Ukip, but lamented that "he has already shown he lacks the backbone to confront him".
Sked, a history professor at the London School of Economics, also expressed doubt about what Farage could do if he decides to quit as party leader before 2020, as he has previously hinted.
"He has no shame and no ability to do anything else,” Sked said. “He couldn’t go into the City – he was only an unsuccessful commodity broker. He would remain as an MEP collecting what he could in salary and expenses in Brussels."
Professor Alan Sked, Ukip's founder and first leader
In response, a Ukip spokesman said: "One has to question the motivations, if not the manners of an increasingly bitter and disappointed man. Just as in the case of Ted Heath there is nothing that rankles as much as an opponent's success."
Sked has been an outspoken critic of Ukip under Farage's leadership, variously describing him as a "dim, racist alcoholic", a "fantasist" and a "none too bright bar-room bore".
See more on General Election 2015
Meanwhile Farage, in his memoirs "Flying Free", described Sked as "soft, unworldly and strangely spoiled", adding: "I suspect that, by appealing as any democratic political party must, to all and sundry... we have tainted SKed's lovely, pure, nineteenth-century vision of his [Anti-Federalist] League and brought him, to his mind at least, into disrepute amongst its academic peers".