The suspect in the killing of the MP David Amess received extensive support under the government’s Channel counter-terrorism programme before his case was closed, the Guardian has learned.

Ali Harbi Ali was first referred to Prevent, the early intervention scheme designed to turn people away from the risk of supporting violence, as a teenager in 2014.

Each year a small proportion of the thousands referred to Prevent are then referred to the Channel programme for more intensive support, overseen by a panel with expertise in deradicalisation and helping those deemed vulnerable to being drawn into terrorism. Both programmes are voluntary and do not involve criminal sanctions.

Ali’s months-long referral to Channel may raise questions for ministers, police and security services. Officials point out that seven years elapsed between him being on Channel and being arrested on Friday on suspicion of murder and believe his engagement with Channel was properly handled.

Ali was referred to the scheme while he was attending an educational establishment in London in 2014 over concerns about him being drawn towards an Islamist ideology. A source with knowledge of the case said: “He went through the process and was discharged.”

He was among the higher cohort of concern of people referred to Prevent. He voluntarily accepted referral to the scheme and went though its processes. This involved having his vulnerability assessed and accepting support, the source said, adding: “He was not thought to pose a threat of terrorist violence and the case was closed.”

Official guidance says individuals with a “terrorism vulnerability” should be helped by Channel while those who are thought to pose a “terrorism risk” require action to be taken by police. The source said: “If we can stop people at a young age becoming criminals, that is good for society and for them.”

In the year to March 2020 there were 6,287 referrals to Prevent and 1,424 referrals to a Channel panel, 697 of which were adopted because of concerns an individual was at risk of radicalisation.

Ali’s father is said by friends and former colleagues to have been an outspoken critic of terrorism during his time as a senior official in the Somalian government. That has compounded the family’s shock after Ali’s arrest at the scene where Amess was repeatedly stabbed while holding a constituency surgery at a church.

Amess was a Conservative MP in Essex for 38 years. His killing has been declared a suspected terrorist incident by police.

Ministers have commissioned a review of the Prevent and Channel programmes, led by William Shawcross, a former head of the Charity Commission. Leaks on Monday suggested it would be fast-tracked in the light of Amess’s death, with proposals to make it more security-oriented, giving police a greater role in panels drawing up intervention schemes and expanding the role of the intelligence agency MI5.

But several in the policing and intelligence community expressed scepticism about that approach. Sir Peter Fahy, the former chief constable of Greater Manchester police who was national lead for Prevent, said he was worried it could deter families and institutions from reporting concerns if the security involvement was more explicit.

“The danger is greater police involvement damages the confidence of families and friends and education professionals to make referrals, if they think it is more likely to go down the law enforcement and intelligence route,” he said.

“We have been trying to stress that Prevent is about safeguarding. If there is a stronger police involvement it makes it less like safeguarding and closer to intelligence gathering or investigative basis for the programme.”

MI5 has been keen to operate at arm’s length from Prevent. A person who has worked closely with the intelligence agencies in the past said that if sharing information about individuals with the security service became the norm “it is not easy to see why people should cooperate with it”.

Muslim communities have made a string of criticisms of Prevent, arguing it unfairly targets them and has encouraged trivial referrals, including against children. In June it emerged that an 11-year-old primary school pupil was referred to Prevent after a teacher mistook the word “alms” for “arms” when the boy said he wanted to give “alms to the oppressed”.