The UK’s main prison-based deradicalisation programme was seen as open to manipulation by convicted terrorists who wanted to avoid official scrutiny on their release, a former government adviser said on Thursday. Ian Acheson, who carried out a review of Islamist extremism in prisons for the government, said his 2016 study revealed that the psychological programme was “easy to game” but his concerns were not included in a summary version of the report released to the public. Mr Acheson’s comments came after the man behind the convict-focused Health Identity Intervention programme (HII) told the BBC there was no guarantee of its success and said that some terrorists regressed while going through the programme. Britain’s success in shifting the motivations of hard-core extremists has come under scrutiny after it emerged that Usman Khan, a former prisoner who stabbed to death two people in November, had been on two programmes aimed at addressing his extremism. Khan, 27, was jailed in 2012 over an Al Qaeda-inspired plot to bomb the UK’s stock exchange and was released in December 2018. He joined a second deradicalisation programme on his release and claimed to have renounced violence but months later carried out the murderous attack. While in prison, he joined the HII programme where participants are encouraged to talk about their beliefs and identity, Christopher Dean told the BBC. “Sometimes people move up two rungs, sometimes individuals may say I've had my doubts about this or that and they may be willing to speak to people, but equally they may go down rungs as well,” he said. “They may come into contact with individuals, they may go through a spell in life where they may feel let's say aggrieved again, where they may begin to re-engage with groups or causes or ideologies associated with their offending behaviour.” Mr Dean published a paper in 2014 outlining his work in which he said that the impact had been “largely positive” but depending on factors including those doing the work and the nature of the offender. But Mr Acheson, a former prison governor, said research for his 2016 report suggested there had been a “degree of false compliance… which meant that it would appear that people had improved or made progress when in fact they might simply have been disguising their intentions in order for attention to pass on to someone else.” He told the BBC that society had to recognise that some offenders were “ideologically bulletproof” and would never change their ways. The government’s own analysis of the programme included interviews with 22 people who went through the programme, including 14 Al Qaeda sympathisers. It said a survey found that the programme was “useful for addressing extremist offending” but the 2018 report did not examine whether or not it worked. Mr Dean said that too few people had been put through the programme to make a scientifically-robust assessment of its effectiveness. Some 224 people were held in prisons in Great Britain for terrorist offences in September 2019 with three-quarters of those Islamist extremists. Khan was among more than 50 terrorist prisoners released in the year to June 2019. Questions over HII followed comments by a former mentor of Usman Khan who claimed last month that authorities ignored his warnings he might have faked his renunciation of violence. The former policeman, who was not identified, told The Sunday Times that Khan had a “suspiciously rehearsed” persona of a reformed extremist during their hours of discussions. Eight months later, Khan stabbed two people to death at a conference on rehabilitation before being chased and tackled to the ground by people from the meeting. Khan, who was wearing a fake suicide vest, was shot dead by police on London Bridge. The government responded to the murders by saying it would introduce tough new sentencing laws to ensure that terrorists served longer in prison.