A UKIP MEP has quit the party in protest at leader Gerard Batten's decision to employ Tommy Robinson as an adviser.
Patrick O'Flynn, a former political editor of the Daily Express, said that under Batten the party had become "an impediment to the Brexit campaigning that I have energetically pursued for many years".
He attacked the decision to employ Robinson, suggesting the UKIP leader had "an apparent and growing fixation" with the co-founder of the English Defence League.
O'Flynn, who has represented the East of England since 2014, said that he was quitting to join the Social Democratic Party.
His departure follows criticism by ex-leader Nigel Farage of the decision to hire Robinson, real name Stephen Yaxley-Lennon, in a role advising Batten on rape gangs and prison reform.
Farage denounced Mr Robinson as a "thug".
Brexit voters have been 'betrayed by establishment parties'
In a statement on his website O'Flynn attacked the decision to align with Robinson, including in an upcoming Brexit protest, saying: "Without any mandate from the membership or the party's elected ruling body to go down this path, Gerard is transforming what UKIP stands for and offers to voters.
"Many long-standing party members have already left as a result.
"Today I am joining them because I have reached the sorry conclusion that UKIP under its current direction and at this decisive moment has become an impediment to the Brexit campaigning that I have energetically pursued for many years.
"The key question in British politics now is which party are millions of sensible, moderate Brexit voters betrayed by establishment parties but wishing no tie-up with Tommy Robinson supposed to vote for?
"The answer, alas, is clearly not UKIP."
Last week Farage said he would write to UKIP's ruling National Executive Committee to demand a vote of no confidence to remove Batten as leader, saying he was damaging both the party and the Brexit cause.
He described Robinson as "a man who's done four prison sentences, lives under a pseudonym and wherever he goes there's violence".
But Batten defended his decision, saying he was “bemused” that Farage “has such concern for the party now when he walked away two years ago.”
The decision was announced shortly after UKIP's NEC voted not to stage a ballot on whether to allow Robinson to join the party.
Watch: UKIP leader Gerard Batten defending the appointment of Tommy Robinson as an advisor
Batten attacked the charges against Robinson as “bogus”.
Talking to talkRADIO’s Matthew Wright, Batten said: “I’ve got tremendous faith in the English justice system, but that doesn’t mean it doesn’t make some terrible mistakes sometimes.
“If you read out his charge sheet, if you read his book Enemy of the State, people who want to do that understand a lot of these charges are not quite kosher, if I can use that word. Some of these charges are a bit bogus.”
Robinson has been jailed three times, once for assault in 2005, again in 2012 for illegally entering the US on a false passport, and once again in 2014 for mortgage fraud.
In 2017 he was handed a suspended sentence for contempt of court, for filming inside Canterbury Crown Court during a rape trial.
In May this year, he was imprisoned for contempt of court for live-streaming outside a rape trial at Leeds Crown Court.
However, he was released earlier this year after he appealed and the case has been referred to the Attorney General in November.