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 Mr 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 Mr Robinson, suggesting the Ukip leader had “an apparent and growing fixation” with the co-founder of the English Defence League.

Mr 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 Mr Robinson, real name Stephen Yaxley-Lennon, in a role advising Mr Batten on rape gangs and prison reform.

Mr Farage denounced Mr Robinson as a “thug”.

In a statement on his website Mr O’Flynn attacked the decision to align with Mr 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 Mr Farage said he would write to Ukip’s ruling National Executive Committee to demand a vote of no confidence to remove Mr Batten as leader, saying he was damaging both the party and the Brexit cause.

He described Mr Robinson as “a man who’s done four prison sentences, lives under a pseudonym and wherever he goes there’s violence”.

But Mr Batten defended his decision, describing Mr Robinson as “courageous”.

The decision was announced shortly after Ukip’s NEC voted not to stage a ballot on whether to allow Mr Robinson to join the party.

Mr Batten denied moving Ukip to the extremes or opening its doors to racists, and told the BBC Mr Robinson would help him turn the party into a “mass movement … a party for ordinary people”.