THE knife-wielding terrorist who was shot dead in Streatham this week was wearing a fake suicide vest. So was the jihadist who killed two prison reform researchers in Fishmongers’ Hall (News, 6 December). So were the three Islamist killers in the Borough Market/London Bridge attack. So were the two inmates who attacked officers inside HM Prison Whitemoor. A number of theories have been offered in explanation.

Initially, it was said that the phoney explosives were designed to deter members of the public from tackling the terrorists. Then it was said that the jihadis were trying to protect themselves from being shot by the police. Most recently, the theory has been advanced that, on the contrary, the men were encouraging the police to open fire so that they could become martyrs to Islam in what has been dubbed “suicide by cop”.

This last idea is the most disturbing, but it fits the facts. A study by Professor Olivier Roy, a French academic, has shown that, in the 20-year period up to the Bataclan massacre (News, 20 November 2015), almost every terrorist in France blew themselves up or got themselves killed by the police. Many quoted the voice message left by Osama bin Laden in the aftermath of 9/11, when he stated: “We love death as you love life”.

All that might seem to justify Boris Johnson’s decision to put an end to the practice of releasing terrorists after they have served half their prison sentence. That may keep the public safe for a little while longer. But it does not solve the real problem, which is that, when these convicts are eventually released from jail, the threat that they pose will be undiminished. It may even be intensified.

Individuals with a distorted notion of Islam need to be brought face to face with the true message of the religion that they purport to embrace. They need a deeper education in the faith; so that they see that their previous theological rationalisation for violence is a perversion. Instead, many find that their radicalisation is intensified by being thrown together in prison with others of the same ilk. They can come out worse than they went in.

Professor Roy’s study suggests, however, that these are not religious fundamentalists who turn to violence. Rather, they are violent nihilists who adopt Islam as the vehicle for their dysfunction and discontent. Some 25 per cent of European jihadists are converts. The profile of the others is far from religious: they are typically the children of immigrants, initially well integrated, living a highly secular life — clubbing, drinking alcohol, having sex, getting involved in drug dealing and acts of violence — who suddenly become “born-again Muslims” after being radicalised on the internet or in small groups rather than community mosques.

Such individuals may need locking up, but, once inside, they need religious rehabilitation, psychological treatment, and an education which resocialises them. Once released, they need the support of the probation services, which have been devastated by public-spending cuts.

Forceful Conservative law-and-order responses will not be sufficient to undo the damage done by decades of Tory austerity. Prisons must not only be places of retribution: they must be places of redemption. If Mr Johnson does not address this, he will not be solving the problem — he will merely be postponing it.

Jihad and Death: The global appeal of Islamic State, by Olivier Roy is published by Hurst