According to Hope Not Hate, a group named the Misanthropic Division, which is linked to the Azov battalion, is working with representatives of UK-based far-right groups, including the proscribed terror organisation National Action and a London-based Polish ultra-nationalist group, to recruit activists to travel to Ukraine.

However, Hope Not Hate said it believed only two or three people had so far left Britain to fight in Ukraine, “and it appears none came via the ranks of the established far right”.

But Rowley underlined the threat posed by such links in a speech on Monday, saying of National Action: “For the first time we have a home-grown, proscribed, white supremacist, neo-Nazi terror group, which seeks to plan attacks and build international networks.”

Releasing its annual State of Hate report on Friday, Hope Not Hate put membership of UK far-right groups at 600-700 people, significantly lower than at times in the past, and said “traditional far-right parties like the British National Party and the National Front are now almost extinct”.

“There is a paradox to the far right in Britain today. Organisationally, the movement is weaker than it has been for 25 years,” the watchdog said. “Yet, at the same time, the far right poses a bigger threat – in terms of violence and promotion of its vile views, particularly anti-Muslim views, than it has in many years.

“The threat is evolving. As traditional British far-right groups collapse, far-right-inspired terrorism is on the rise. Replacing old-fashioned racial nationalism is anti-Muslim hatred. Today’s key activists tend to be younger, operate online and have little of the obvious ‘Nazi’ baggage of their predecessors.”

The Hope Not Hate report identifies an “emerging younger generation of far-right activists who are tech savvy, avoid the stereotyped ‘looks’ of the past, and are growing in size and influence”.

The watchdog’s chief executive, Nick Lowles, said: “Coupled with the collapse of the British National Party, which has convinced some hardliners that there is now no parliamentary route to fascism, and the Islamist terrorist attacks last year which led directly to four terrorist attacks or attempted attacks in response, and a worsening public perception of British Muslims and Islam generally, we must be prepared for more terrorist plots and use of extreme violence from the far right for the foreseeable future.”

In his speech on Monday, Rowley said: “The rightwing threat was not previously organised. Every now and then, there’s been an individual motivated by that rhetoric who has committed a terrorist act. But we’ve not had an organised rightwing threat like we do now.”

In February, Darren Osborne was jailed for life after being convicted of carrying out a terror attack on Muslims in Finsbury Park, north London, in 2017. The jury heard he had become radicalised over just a few weeks by content posted online by figures such as the former English Defence League leader Tommy Robinson, as well as Britain First and other groups.

In a statement, Ben Wallace, the UK’s security minister, said: “This government did not hesitate to proscribe a neo-Nazi group, National Action, when the evidence was enough, and we will not hesitate to take further action. We have continued to enforce this by proscribing National Action’s known aliases, Scottish Dawn and NS131 as well.

“Through our Prevent strategy, we are successfully fighting back against the terrorist recruiters and safeguarding vulnerable people who are being preyed upon – whether by Islamists, neo-Nazis or other violent extremists. At its heart, this report shines a light on the growth of intolerance across the UK and Europe and we should all take a stand against extremism, whether it is expressed by far right, Islamist groups or other movements.”