Ukip’s membership has soared by 15% in a month, insiders have revealed, raising the prospect of a return to the mainstream of a party still publicly associated with Brexit, but which has recently taken a more hard-right nationalist stance.

The arrival of nearly 3,200 new members in July, and a boost in the pollsfrom around 2% to 5% or more, follows Theresa May’s Chequers plan. Senior Ukip members say they believe many people are returning from the Conservatives.

This sets up a possible battle for supremacy in a party which under the leadership of Gerard Batten has talked more in recent months about Islam than Brexit, and now has close links to Tommy Robinson, the far-right activist released from prison on Wednesday.

Batten, who took over in February, refers to Islam as a “death cult” and has called the prophet Muhammad a paedophile. He has also likened Robinson, the founder of the English Defence League, to Gandhi and Nelson Mandela, saying he is “on the right side of a great cause in a struggle between good and evil”.

This embrace has prompted disquiet among some senior Ukip members, as has Batten’s decision to welcome a trio of controversial social media activists into the party, including from the far-right website Infowars.

One party figure, who asked to not be named, said some MEPs and other senior members had urged Batten to tone down his hard-right rhetoric and focus more on disaffection about the Chequers plan.

“It seems ludicrous to be talking about anything other than Brexit at the moment,” the figure said. “We’ve all got our personal policy interests, but this is the only subject in town right now.”

Another senior member said Batten’s stance had brought certain MEPs close to quitting. “Some people don’t like at all where Gerard is taking the party, but they’re keeping quiet because of Chequers,” they said. “It also seems likely that some of the new members don’t quite realise what sort of party Ukip is now.”

The resurgence is relative. At about 24,000, membership is still less than half of its peak of 46,000 in mid-2015. However, it is a welcome boost for a party that has lurched from crisis to crisis, and took just 1.8% of the vote in last year’s general election.

A complicating factor is that not all the new members will be motivated by Brexit. The party has attracted new interest from younger people following the endorsement of the three popular YouTube-based activists. These include Paul Joseph Watson of Infowars, a US website which has argued the Sandy Hook elementary school shooting was a hoax involving child actors.

It means that if others in the party did want a change in direction – even Nigel Farage, who has pledged to return to frontline politics next year if he feels Brexit is being thwarted – they might struggle to wrest back control.

“There’s enough people in Ukip now who follow Gerard’s line,” the first senior source said. “It would take a lot of organisation to turn the party round, and it doesn’t currently exist. Instead you’ll probably have two parties in one. Those following Gerard’s views and the people there for Brexit and the Chequers deal.”

If Batten remains in charge and Ukip continues to prosper, pressure groups say the party could become the UK’s first modern hard-right political force to join the mainstream, similar to the National Rally, formerly the National Front, in France, or Alternative for Germany (AfD).

Some within Ukip have reportedly held talks with Steve Bannon, Donald Trump’s former chief strategist, who has pledged to work with populist and far-right parties across Europe.

Batten declined to talk to the Guardian, and a party spokesman said the paper was on a list of “biased media” to which it will no longer comment.

At a rally in support of Robinson in London earlier this month, however, Batten reiterated his hardline anti-Islam stance. “I want our descendants to be free, not to live under Islamic ideology,” he said.

Batten told the crowd: “The founder of their cult was himself a paedophile and kept sex slaves. And yet he is held up to be the perfect model of a man for all time. But we, the infidels and the kafirs, are not supposed to talk about it.”

Nick Ryan from Hope Not Hate, which tracks far-right groups, said such views, coupled with existing community tensions and potential disaffection over Brexit, could bring “potent conditions for a radical right movement to try and take advantage of the inevitable anger which will occur”.

Matthew Goodwin, a professor of politics at Kent University, who has studied Ukip closely, takes a different view. He said links to Robinson and Infowars could bar a return to mainstream support for a party that won almost 4m votes in the 2015 election.

“As a 5% to 15% party I think there will be space for Ukip among disgruntled Conservatives, immigration-minded blue-collar workers and older voters,” he said.

“But in order for Ukip to ever get to be a 20% to 25% party, which it did manage to do in the past, it’s going to have to have a charismatic leader, dissociate itself from stigma and look relatively mainstream and acceptable, in particular for the middle class.”

Peter Walker

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