Up to seven in 10 people referred to the official scheme intended to stop people becoming terrorists may suffer from mental ill health or other vulnerabilities that could leave them prone to falling for propaganda from violent extremists.

Simon Cole, a chief constable and the police lead for Prevent, said such psychological problems were much more of a potential factor than first thought.

Three special hubs in London, the Midlands and the north-west are seeing people missed by other services, with the counter-terrorism scheme being the first state service to refer them for the help they may need, police say.

Simon Cole said a significant proportion of those seen by Prevent had complex needs.

Cole also said increasing numbers of children were being radicalised by banned neo-Nazi groups, which deliberately try to recruit the young and vulnerable in their bedrooms in order to turn them into foot soldiers in a race war.

Counter-terrorism policing has been working for several years with health professionals to see how many people being referred to Prevent may have mental health issues or vulnerabilities such as autism spectrum disorder, alcohol abuse issues, drug problems or homelessness.

The three hubs were set up to deal with those with mental health issues but, as more people were assessed, adapted to deal with other vulnerabilities that could cause mental health distress.

Prevent is a voluntary scheme that has been dogged by controversy. It aims to identify people who may be at risk of committing terrorist crimes, and divert them. In 2016, Cole said 44% of the individuals involved had mental health or psychological problems – but the figure is now far higher.

Cole said about 70% of Prevent cases “now have some measure of concern within them that needs assessing via vulnerability support hub.

“If a person is vulnerable for whatever reason, they might find the sort of ideologies around radicalisation something that they feel gives them some measure of value.”

He added: “It could be that people who have vulnerabilities are seeking self-identification through being linked across to radicalisation. The vulnerability support hubs are an important part because what it ensures … is that appropriate support can be brought alongside people so that if there are mental health needs, they can be met.”

Cole said a significant proportion of those seen by Prevent had complex needs. “About 40% of those, there’s multiple factors. So that might be substance misuse or housing or other offending behaviours [such as violence]. You would have heard the independent terrorist reviewer talk a few weeks ago about autism specifically. So we have seen that the early thinking has been borne out as we’ve gone forward.”

Police are also increasingly worried about radicalisation of children, especially by the far right. In the last financial year, 21 children were arrested for terrorism, 15 of them on suspicion of involvement in extreme rightwing terrorism. In total, 13% of arrests for terrorism in the last financial year were of youths under 18, compared with 5% in the previous year. Young people under the age of 24 accounted for nearly 60% of extreme rightwing terror arrests, a rapid rise.

Cole said: “Certainly we’re seeing some young people being, in effect, groomed online, through things like gaming sites, and then being moved into the more private spaces of the web where that process is continuing. There is some deliberate targeting there.”

Although the scheme is accused by some of unfairly targeting Muslim communities, it is increasingly having to make parents in white communities aware of the dangers of radicalisation as the far-right threat grows. Prevent will also increase its focus on parents, such as its recent sponsorship tie-up with the parenting website Netmums.

The clinician in charge of the vulnerability support services, Dr Nicki Fowler, said support for violence was a symptom of a deeper problem. “When people get involved with extremism or any type of risky behaviour, it is usually their solution, not their problem.”

She said people could be lured by extremist narratives blaming problems on certain groups with the message: “Come and join our group, it’s not your fault, it’s their fault.”

Problems with housing, for example, may cause psychological distress or anxiety, which the hubs aim to work on. Fowler said mental health distress was one of many factors that affected the risk of believing in terrorist violence. “Most commonly it’s relevant as part of many factors.”

She added: “Sometimes it’s present and completely irrelevant.”

Prevent rarely escapes controversy, such as accusations of invading privacy or tarnishing communities, which it denies. Fowler said police did not have access to clinical notes or sensitive health information about individuals referred to the hubs.

Ch Supt Nik Adams, the national coordinator for Prevent, said police were not trawling for mental health information. Instead, once people are in Prevent, they are offered mental health treatment and support for their needs, which have often often gone undetected.

Adams said: “There is a rich pool of vulnerabilities and people out there who can be exploited. And our job is to identify those that are susceptible and vulnerable and to seek to intervene and offer them support in a way that keeps them and others safe.”

For Prevent, referrals over concerns about Islamist (24%) and extreme rightwing terrorist (22%) vulnerability are broadly level, but the single biggest group is mixed, unstable and unclear ideologies, at 51%.

“There are more people whose motivation isn’t as clear within the people referred into Prevent,” Cole said.

Generally, the level of police and MI5 operations investigating those suspected of actual involvement in terrorism runs at six Islamist investigations to every one extreme rightwing investigation.

In 2019 the assistant commissioner Neil Basu, until last month the head of counter-terrorism, said Prevent was the most important plank of Britain’s counter-terrorism strategy, but had been “badly handled” and had to become more transparent and community-led.