More than 100 convicted and suspected terrorists living in the community are subject to a secretive government programme designed to stop the most entrenched extremists from endangering the public, the Guardian can reveal.

The Home Office twice refused a Freedom of Information request by the Guardian but following a complaint to the data watchdog, the Information Commissioner’s Office, revealed that 116 people were subject to the desistance and disengagement programme (DDP) between October 2016 and September 2018.

The release shows 30 individuals were enrolled from October 2016 to September 2017 and this nearly tripled in the year to September 2018 to 86. However, the first year was a trial of the programme, accounting for the sharp increase in the following year.

Little is known about the DDP, although the government has made expanding the programme a key component of its refreshed counter-terrorism strategy.

The programme, running since October 2016 as an arm of Prevent, targets all terrorism and terrorism-related offenders released from prison on probation licence. Anjem Choudary, the Islamist firebrand preacher, is reportedly a DDP subject.

In addition, the DDP covers returnees from conflict zones in Syria or Iraq who are subject to a temporary exclusion order (TEO), which makes it unlawful for an individual to return to the UK without engagement with the authorities.

Individuals subject to terrorism prevention and investigation measures (Tpims) – orders used to restrict people who are deemed a threat but cannot be prosecuted or deported if they are a foreign national – are also subject to the programme.

The numbers roughly fit with official figures that show there were 96 prisoners convicted of terrorism offences released in 2017 and 2018. Nine people were subject to TEOs in 2017; figures are not yet available for 2018.

In the government’s official counter-terrorism strategy, Contest, it describes the DDP: “Through the DDP, we provide a range of intensive, tailored interventions and practical support, designed to tackle the drivers of radicalisation around universal needs for identity, self-esteem, meaning and purpose; as well as to address personal grievances that the extremist narrative has exacerbated.

“Support could include mentoring, psychological support, theological and ideological advice.”

The Home Office hopes to double the number subject to the programme to 230 by June this year.

Rajan Basra, a research fellow at the International Centre for the Study of Radicalisation (ICSR) at King’s College London, said: “Little information exists in the public domain on the DDP, but the general aim is to offer a more holistic approach to disengagement.

“It recognises that disengagement from extremism isn’t just about ideology, and so the programme offers mentoring, family support, and other personal help alongside the theological input.

“Even then, there’s no set formula for disengagement from extremism; it’s usually a gradual process, and given the varied challenges – which range from returnees from Syria to the homegrown radicalisation of jihadists as well as an emergent far-right – it requires resources, time, and patience.

“The Home Office doesn’t release information on how successful it has been, though it’s important to remember that it’s still a relatively new program. It can take time to figure out what works, especially when each case is unique and in need of a tailored approach.

“This issue is one that all of Europe is facing, where we’re seeing record numbers of extremists in prison, as well as the prospect of additional returnees from Syria. Those who have engaged in terrorism will eventually be released, so in anticipation we have to ask what are the most effective ways of managing the risks they pose.”

The case of Shamima Begum, the teenage girl who fled her east London family for Syria after reading terrorist propaganda online, saw the issue of how to deal with returnees from Syria and Iraq subject to renewed scrutiny.

Begum, who married an Isis fighter and had three children, all of whom died as infants, was stripped of her British citizenship and is living in a Syrian refugee camp.

Similarly, the release of Choudary raised questions over how individuals convicted of terrorist offences are managed in the community. It is understood Choudary is among the 116 enrolled on the DDP.

Prevent also includes Channel, a voluntary programme designed for people showing signs of extremism who are yet to meet a criminal threshold. It is understood the DDP is mandatory.

Raffaello Pantucci​, director in International Security Studies at the Royal United Services Institute (RUSI), said: “Channel is voluntary. They do that because if they force people to do these things they don’t always work. If someone doesn’t want to reject these ideas or get onto a different track, that’s quite difficult to do. Channel is about stopping people before they got there.

“If they’ve already been radicalised and involved in terrorist activity then you’re talking about making sure they don’t re-engage with it’; that’s what the DDP is about. Making that mandatory makes sense.”

He added: “People have realised trying to persuade someone to reject a fundamental idea they’ve absorbed is really difficult.

“If we can steer a person away from what they’re doing – they’re often dealing with young men in an excitable moment of their lives – if you can give them something else to fill their time with that’s better. It’s same as an approach you see with gangs.”

Last year, Guardian analysis revealed that police and security services face a surge in the number of convicted terrorists released from prison, raising questions about how such figures are managed in the community. More than 80 of the 193 terms issued for terrorism offences between 2007 and 2016 were completed by the end of last year. However, the number of individuals released could be much higher as prisoners are eligible for release halfway through their sentence.

Melindy Brown, a lecturer in criminology at Birmingham City University, said measuring the success of programmes such as the DDP was complicated.

“Because the DDP is quite secretive it’s quite difficult to say if it’s been effective,” Brown said. “The fact it is still in place … is a suggestion it’s obviously doing something right.

“But previously, anything that has been done in terms of disengagement and reintegration of people, there haven’t really been any examples of anything that can truly say it has stopped someone from not engaging in that sort of behaviour.

“How do we know if someone has truly desisted from a crime?”

A Home Office spokesperson said: “Keeping the public safe is our first priority and an important part of this is working with individuals who have been radicalised to reintegrate them safely back into society.