A hard core of fascist extremists in Britain are prepared to murder and commit acts of terror, and have strong links to groups overseas, observers of the domestic far-right have told the Guardian.

As the government’s joint terrorism analysis centre reportedly begins a review of the threat posed by British rightwing extremists, spurred by the conviction of Darren Osborne, between 50 and 60 people remain prepared to carry out acts of violence, one expert says.

Matthew Collins, the head of research at Hope Not Hate, said groups such as National Action had evolved beyond neo-Nazi ideology to espouse a violent extremism influenced by the Islamist terrorism they purport to oppose.

“They model themselves on jihad, that’s quite clear,” Collins said. “We no longer believe that they are neo-Nazis, although they are certainly still racists. We believe that they are nihilists, partly because they are so obsessed by terror and the secrecy of terror.”

According to Hope Not Hate’s research, National Action has also drawn from the methods and ideas of the leftwing Baader-Meinhof gang, and studied IRA cell structures. “They started off like naughty boy scouts, but they had a massive schism in 2016,” Collins said.

“A group broke away who said they were acting like terrorists, talking like terrorists and being painted like terrorists, so why don’t [they] become terrorists.”

Collins said he believed the police and security services had little understanding of the nature of National Action and related groups. But Gerry Gable, the editor of Searchlight magazine, which tracks the far-right, said he believed that MI5 and MI6 knew more than they had let on.

“MI6 know what’s going on, and for their own reasons they don’t act on a lot of stuff,” he said. In the past, the security services had operated some groups, such as Combat 18, as honeypots to draw out hardliners. Groups operating in recent years whose leaders appeared to have excellent luck in the courts and with the police could be operating in the same way, he added.