The Ukip leader, Gerard Batten, has appointed the anti-lslam activist Tommy Robinson as an official adviser, further cementing the party’s move towards the far right.

Batten said the founder of the far-right activist group the English Defence League, whose real name is Stephen Yaxley-Lennon, would advise him on grooming gangs and prisons.

The Ukip leader said Robinson, who faces a possible retrial after successfully appealing against a jail term for contempt of court for live-streaming videos to Facebook from outside a grooming gang case, had “great knowledge” about the subjects.

This week Ukip announced that Batten had formally sought to begin the process to allow Robinson to become a member. He is currently not allowed as current and former EDL members are banned under existing Ukip rules to keep out entrants from the far right. The move was resisted by the party’s national executive, who said any decision on the issue should be postponed until after Brexit day in March.

Batten, who took over as leader following the departure of Henry Bolton this year, is open about his anti-Islamic views, calling the religion a “death cult”, and has suggested that UK Muslims should be asked to sign a declaration renouncing elements of the Qur’an.

He has sought to move Ukip towards a more anti-Islam stance. A new set of policies unveiled in the autumn included a mooted halt on immigration from Islamic countries and the possibility of separate jails for Muslim prisoners.

Batten said: “I have appointed Tommy Robinson to be a personal special adviser on two subjects which he has great knowledge. It is not necessary for him to be a party member in order to assist me in this role. I am looking forward to working with him.”

Robinson has convictions for assault, drugs and public order offences, and has been jailed for mortgage fraud and for using someone else’s passport to travel to the US. He is awaiting a decision on his contempt of court retrial, which was referred last month to the attorney general for review.

He has sought to reinvent himself as a “campaigner” against Muslim gangs who groom girls for sex, which has attracted him a large and fervent audience. Batten has previously spoken at his rallies, and compared Robinson to Gandhi and Nelson Mandela.

Critics of Robinson’s actions describe him as an opportunist who has used the grooming issue to promote a more general far-right, anti-Islam agenda and push his personal brand.

Batten, who initially said he would serve only as interim leader, has seen a series of his fellow Ukip MEPs quit over his push towards the far right.

Some senior party figures have urged him to focus instead on campaigning against Theresa May’s Brexit plans, opposition to which has helped push Ukip support up to 8% in some polls.

• This article was amended on 23 November 2018 to note that both current and former EDL members are barred from joining Ukip under the party’s rules.