More than 80 per cent of under-18s arrested for terrorism last year were linked to extreme right-wing beliefs, police figures show.

This compares with just 20 per cent across all age groups, with the majority of counter-terror and extremism investigations still focusing on Islamist-inspired threats.

Home Office data shows a similar sharp rise in the number of under-18s – including some under 10 – referred to the Government’s counter-terrorism programme over concerns about their possible involvement with the far-right.

A total of 682 children were referred for this reason in 2017-18, compared with 131 in 2014-15 – a more than five-fold increase, according to figures obtained through a freedom of information request.

The total for 2017-18 includes 24 children under the age of 10.

A former neo-Nazi who runs a group that helps people leave far-right organisations said video games and extremist content on social media were being used to recruit children.

Nigel Bromage, the founder of Exit UK, told Sky News that child-specific content being used by the far right to target youngsters online include "shoot ’em up" video games, memes and videos.

Neil Basu, the head of UK counter-terrorism policing, said that while Islamist terrorism remained the greatest threat and makes up 80 per cent of his workload, right-wing extremism is the fastest growing threat and has grown from six to 10 per cent of his work in the past few years.

He said: "There has definitely been a growth in nationalistic material online, white supremacist literature, things that are extremely disturbing in the extreme right-wing space, many of which do hit criminal thresholds, some of which is designed to entice people into closed groups where criminality and Nazi ideology is being discussed. 

"It does seem to be having an effect on younger and younger children. In our case work in the extreme right-wing space, the subjects of interest to us do appear to be younger.

"My warning has always been that the Islamist threat is still the greatest threat we face, but the one that’s growing fastest, from a relatively low base, is the right-wing terrorism threat."

A new website is being launched to help concerned parents get advice on how to deal with teenagers who may be showing signs of radicalisation.