UKIP leader Gerard Batten has accused Nigel Farage of "sour grapes" for quitting the party over concerns about its direction soon after far-right activist Tommy Robinson was appointed as an adviser.
Mr Farage - UKIP's former leader - said earlier this week that Mr Batten was "obsessed" with the issue of Islam as well as ex-English Defence League (EDL) leader Mr Robinson.
But Mr Batten told Sky News his former colleague was merely "looking for an excuse" to leave UKIP after Mr Farage "failed dismally" to bring a vote of no confidence against him.
He said: "Nigel obviously hasn't read the manifesto that we published in September because there aren't any anti-Muslim policies in there and there wouldn't be because we're not anti-Muslim.
"I think this is just sour grapes, he's been looking for an excuse to walk away for two years and now he's found it."
Mr Batten also revealed Mr Robinson, whose real name is Stephen Yaxley-Lennon, would be advising him on prisons.
His appointment comes after the former EDL leader was released from prison in August after the Court of Appeal quashed a contempt of court finding made at Leeds Crown Court.
The case has been referred to the attorney general.
Mr Batten said: "He's told me already about how they're run - the prisoners run the prisons, they're run by prison gangs, drugs are rife in prisons.
"Prison officers are bribed to bring in telephones and drugs.
"He [Robinson] wasn't in solitary confinement, people were talking to him through the bars, telling him they were going to kill him, which is why he couldn't eat the food that was served to him."
Mr Batten said he liked to get advice "first hand from people at the front line".
Turning to Brexit, the UKIP leader called on parliament to "dump the deal" presented by Theresa May.
He said: "We're not leaving, we're going to continue under this transition period, the so-called backstop that we can't get out of because we can't have a unilateral right of withdrawal.
"We're going to continue paying them lots of money, we're going to continue with open borders and the whole thing has been concocted so the political establishment can say it's far too difficult we can't leave so we have to stay in."
Asked if Brexiteers would be falling into a trap if they voted against the deal, risking no Brexit at all, Mr Batten replied by asking: "What is the point in voting for something when you haven't really left anyway?"
He then outlined his vision for how the break from the European bloc should unfold.
"What I've been advocating for 25 years - long before Nigel Farage got on the bandwagon by the way - was unilateral unconditional withdrawal whereby parliament takes control of the process," he said.
"So it repeals the 1972 European Communities Act as the first step, tells the European Union 'we've just left but don't worry because all EU derived law remains in place but we're going to start amending and repealing and we'll tell you how it's going to work' in a cooperative and friendly spirit."
He said he thought the economy would "boom" and the UK would make "enormous savings".