On 29 November 2019, Marc Conway was about to give a speech in London’s Fishmonger’s Hall. Conway, who works for the Prison Reform Trust, had been on a life-changing project while serving time in prison that brought together inmates and Cambridge students. Now it was its fifth anniversary and he had been asked to say some words at the celebration for it.

But when he stepped out for a cigarette break, another former offender from the course launched a terrorist attack, stabbing two Cambridge graduates dead. Conway was among those who gave chase to the attacker, who was wearing a fake suicide vest, and held him down.

He was lauded as a hero for his bravery. But, Conway says, the whole time he was terrified that his actions could see him recalled to prison.

Like thousands of other offenders, Conway had been sentenced to an IPP – imprisonment for public protection. It meant that although his tariff was five years for armed robbery, he could be held for up to 99 years. In the end he served eight years for that crime, but once released, his IPP also meant he could be recalled for the slightest misdemeanour and held indefinitely.

Guardian features writer Simon Hattenstone explains that a third of IPPs are given for more minor offences, which carry tariffs of less than two years in prison. He tells Michael Safi IPP sentences have long been controversial and were abolished in 2012. But those who were sentenced before that have been left in limbo. Many have taken their own lives.

Now a new bill passing through parliament could make it possible for an IPP to be terminated after five years. Yet campaigners say it does not go far enough and that all those on IPPs should be re-sentenced – and the justice select committee agrees. So why isn’t that being done?

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