One of the frontrunners to become the new Ukip leader has used his official campaign launch to defend Donald Trump and to call for a national referendum on banning women from wearing the niqab.

Speaking in front of a few dozen supporters at a pub in Westminster, Raheem Kassam also appeared to cast doubt on the veracity of women accusing the US Republican presidential candidate of sexual assault, and said he did not believe Trump had anti-Muslim views.

Kassam, 30, a former staffer for Nigel Farage who now runs the UK arm of the rightwing US news network Breitbart, is second favourite with bookmakers behind Paul Nuttall, an MEP and deputy leader, to be voted the next Ukip leader.

Suzanne Evans, a former Conservative councillor who compiled the party’s 2015 election manifesto, is also standing. Farage is the interim leader after his replacement, Diane James, stepped down after 18 days.

Speaking at the central London pub, where he spent much of the time with a pint of beer in his hand, Kassam styled himself as the Farage continuity candidate, while also promising to hugely expand Ukip’s membership and inject radical ideas into the party.

“I regard myself as the Faragist candidate,” he told supporters. “Of the Faragists, I am the Farage-est. And that is something that we as a party should not hide from. Our legacy is Nigel, Nigel is our legacy. And we shouldn’t be trying to drag this party to the squishy centre ground.

“We should be proud of what I call Faragism – a belief in your country, a belief in your culture, a belief in the people of this great nation.”

Kassam’s candidacy has attracted immediate controversy, notably over his prolific and often robust Twitter feed, which has included a deeply personal insult against Nicola Sturgeon, for which he again apologised.

He has also attracted attention for his appreciation of Trump – Kassam’s campaign slogan of “Make Ukip Great Again” echoes the Republican candidate’s motto.

While describing his slogan as “a bit tongue in cheek”, Kassam reiterated that he would supported Trump in the 8 November election, saying: “I hope he wins over crooked Hillary, certainly.”

Kassam told reporters after his speech: “I’m not endorsing him. What I’ve said it that I prefer him to win than Hillary Clinton. I’ve got no problem with endorsing him, it’s just that I don’t think my endorsement makes any difference either way.”

He declined to condemn Trump’s policies, such as the mooted proposal to bar all Muslims from entering the US, saying: “I don’t believe he has anti-Muslim views.” Kassam added: “I can see where his supporters’ frustrations were in supporting the blanket ban, but I think we have a much better plan of how to deal with radical Islam.”

Asked about the series of women who have accused Trump of sexual assault, Kassam said he had doubts about the claims, saying: “I don’t know. I think it’s strange that somebody who was a celebrity for so many years only has these things come out right at the tail end of a presidential campaign.”

It was possible that the women “did not feel that he had enough support to speak out” in the past, he added.

Kassam’s personal manifesto is strongly rightwing, including massive cuts to the foreign aid budget, and a focus on cutting immigration and measures targeting elements of Islam, including an end to forms of halal slaughter.

Kassam, who was brought up in a Muslim family but says he now has no religious faith, said he supported a referendum on banning the use of the niqab, the most conservative form of Islamic dress for women, which covers the face.

“I think most people in this country are OK with the hijab,” he said. “But I would want a referendum on the niqab.”

After James resigned, the immediate favourite to replace her was Steven Woolfe, a former barrister and now an MEP. However, he left the party in the wake of a scuffle with a fellow Ukip MEP, Mike Hookem, amid a dispute about Woolfe’s admission he had almost defected to the Conservatives.

Woolfe spent three days in hospital after the fracas, and said Hookem had punched him. However, a party investigation into the incident said Woolfe appeared primarily to blame.