Thousands of Britons regularly use online forums that espouse rightwing extremism, it has emerged amid fresh warnings that the UK is facing a “new wave” of anti-Muslim hatred.

An indicator of the evolving challenge is the recent move by MI5 to wrest control from the police of investigations into far-right plots that “cross the statutory threshold to be considered terrorism”. The security services are currently investigating potential contact between the Christchurch gunman and rightwing extremists in the UK.

Analysis by anti-fascist charity Hope not Hate indicates that huge numbers of Britons are among the global audience for far-right forums – such as Stormfront, the white supremacist website – that spread extremist ideolology.

Sara Khan, the UK’s lead anti-extremism commissioner, has pointed to a fresh surge of UK-based far-right activists who are, she says, “organised, professional and actively attempting to recruit”.

Khan, who has visited 14 UK towns and cities as she prepares a report on extremism for the home secretary, told the Observer: “I have heard deep concern about the far right and its devastating impact on individuals, communities and our democracy.” A “frightening amount of legal extremist content online” was fuelling far-right activism, she added.

The security services, having placed the threat from rightwing extremist ideology on a par with Islamist and Northern Ireland-related terrorism, have said they are investigating “very sharp high-end cases” in relation to the far right.

So far, though, they have not revealed how many of the 700 or so live terror plots and 20,000 individuals classified as “closed subjects of concern” – people who have previously been investigated and may pose a future threat – are related to rightwing extremism.

However, MI5 said the volume of rightwing cases was “absolutely dwarfed by the number of Islamist cases”.

The government’s latest counter-terrorism assessment does, however, shed interesting light on the evolving far-right threat. Before 2014, it says, extreme rightwing activity in the UK was confined to “small, established groups with an older membership, which promoted anti-immigration and white supremacist views, but presented a very low risk to national security.”

Four extreme rightwing terror plots were foiled in the year to June 2018, fuelling disquiet over online forums and their ability to disseminate extremist ideology.

Joe Mulhall, a researcher for Hope not Hate, said the global audience for chatrooms and messaging sites that effectively and quickly spread hate speech ran into the hundreds of thousands. “We know that because we can look at the forums through which these people engage and see that they have hundreds of thousands of people on them,” he said.

In December, messages left on an online gaming server illustrated the issue: on it, neo-Nazis from Europe and the US, using pseudonyms, exchanged racist views and messages glorifying violence. Some of the chat logs involved members of the Atomwaffen Division, a US group that encourages terrorism, and there was also correspondence about the creation of a new far-right British group called the Sonnenkrieg Division.

Latest figures documenting cases referred to the UK government’s counter-extremism programme corroborating the increased activity of the far right with a 36% rise in tip-offs over rightwing radicalisation.

In the year to March 2018, 1,312 individuals were referred to Prevent, an increase of 36% on the previous year, and accounting for almost a fifth of all referrals. For the first time, a similar percentage of individuals received support from the Channel scheme, which helps people at risk of being drawn into terrorism, over concerns related to Islamist and rightwing extremism.