The number of suspected far-right extremists referred to the Prevent anti-radicalisation programme has increased by more than a quarter, new figures show, as the number of Islamists falls.

Of the total 6,093 people referred in the year to March 2017, 61 per cent (3,704) had raised concern about Islamist extremism, and 16 per cent (943) over far-right extremism.

More than 1,600 children under the age of 15 were flagged as a risk, as well as 1,800 between the ages of 15 and 20 – the largest age group represented.

The overall figure is a decrease on the 7,631 people referred to Prevent in the 2015/16 financial year, when 65 per cent (4,997) were suspected of Islamist extremism and 10 per cent (759) of right-wing extremism.

But the number is believed to have risen in the wake of terror attacks that struck Britain last year, with security services warning of an “unrelenting” threat.

The figures were revealed after police foiled 10 Islamist and four right-wing terror plots, in the same period that saw 36 victims killed and hundreds injured in the Westminster, Manchester, London Bridge, Finsbury Park and Parsons Green attacks.

Mark Rowley, the former head of national counter-terror policing, warned last month that the “right-wing terrorist threat is more significant and more challenging than the public debate gives it credit for”.

His successor, assistant commissioner Neil Basu, told The Independent that the tempo of terror plots remains high, while appealing for public vigilance.

Four far-right UK terrorist plots foiled since Westminster attack, police reveal

“It is possible for attacks to get through, and we’ve seen that in the speed people are radicalised, the speed of which they plan and the speed they commit the crime,” he added. “It’s becoming harder to stop these things.”

Online radicalisation is known to have driven several terror attacks and numerous plots in the UK, with Finsbury Park attacker Darren Osborne consuming posts from Tommy Robinson and Britain First, and Isis-inspired extremists viewing material from the group's extensive propaganda network.

Anyone suspected of being drawn into terrorism must be reported to Prevent under a statutory duty that covers police, teachers, the NHS, prisons, local councils and other authorities.

Teachers and police officers raised the alarm in most cases, passing on details of people they believed were “vulnerable to being drawn into terrorism”.

A third of referees were assessed to require no further action by Prevent. 45 per cent were given help through alternative services like housing and education, and 19 per cent went into the voluntary Channel counter-radicalisation scheme – just 5 per cent of the total.

Almost 60 per cent of people referred were aged 20 or under, and 82 per cent were male, mostly coming from London, followed by the South-east, North-east and North-west.

For the people selected to receive for support from Channel, 37 per cent were from the extreme right-wing, but the statistics showed that a fifth of people dropped out of the process, up from one in six the previous year.

The Home Office said that support from other services remained for some and “any terrorism risk that might be present is managed by the police”, but there are calls for the programme to be made compulsory, amid concerns over the threat posed by foreign fighters returning from Isis territories in Syria and Iraq with their families.

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Under-15s made up largest proportion of Islamist referrals, and 15-20-year-olds for the right-wing.

The statistic reflects mass referrals of family members linked to a known extremist by authorities, activity by schools and the impact of online radicalisation on teenagers and young people.

The Home Office said all cases are screened by police and filtered out if they are based on inaccurate information or part of a terrorism investigation.

An assessment then decides if any action is required, and officials can decide that a person’s vulnerability is not linked to radicalisation and offer them other forms of support.

Education, health and council officials on Channel panels draw up plans to de-radicalise anyone where it is “necessary and proportionate to do so”, including ideological mentoring and help with education, work and mental health.

Meetings are supposed to continue until they are deemed to present no further terror risk, but more than a fifth of people failed to reach the benchmark in 2016/17.

Joe* was referred to the programme after being drawn to the extreme right-wing through older men he met at football matches when he was just 15.

After getting in trouble at school for fights and racist insults against other pupils, he was arrested and flagged to Prevent.

Isis propaganda is believed to be driving the number of children referred to Prevent

“It was easy to get dragged along – there were a lot of people I looked up to and I thought they were positive role models,” he said.

“My mentor Nick helped me to understand both sides of the argument. Before then, I had only seen one side of things that I’d seen or watched online.”

Prevent is also supporting youth groups and schemes for both children and adults to raise awareness of extremist content online. It is pushing for the creation of “counter-narratives” that can be used to combat radical narratives.

The programme – set up over a decade ago as part of the Government’s wider Contest counter-terror strategy – has been dogged by controversy and opposition by groups accusing it of discriminating against Muslims and worsening radicalisation.

It is only the second time has released detailed information on Prevent and the Home Office is hoping to combat suspicion and mistrust while improving engagement.

Ben Wallace, the security minister, said Prevent was “fundamentally about protecting people” from forms of radicalisation, and that it has stopped hundreds of people being drawn towards terrorism and violence.

“The figures released today show that the programme is continuously improving, demonstrated by better referrals being made and the fact that we are tackling the threat from the far-right,” he added.

“We have seen all too starkly the devastating consequences of radicalisation and the need for a coordinated response at a local and national level.

“We will continue to work with partners to improve and make sure this crucial support is given to those who need it.”