A Northern Ireland-born counter-terrorism expert has hit out at the Government in the wake of the latest terror attack.
Sudesh Amman (20) was shot dead by police in London after attacking two bystanders with a knife.
He was under police surveillance after being released from prison days earlier.
Four years ago Professor Ian Acheson, from Enniskillen, led an independent review of Islamist extremism in prisons and probation. Only eight of his team's 69 recommendations were accepted by the authorities.
Speaking of his disappointment at the response, he said: "This implies a continuing serious failure of leadership and will to confront terrorism that I identified."
He said the Streatham High Road attack showed that root and branch changes were still needed in the prison system to protect people from extremists.
Speaking on Monday on Radio 5 Live, he said: "I don't think if you were trying to construct an incubator for violent extremism and radicalisation, you would do much more than create our current prison conditions where violent and credulous young men searching for excitement and meaning are in close proximity to highly charismatic Islamist and right wing extremists who want to seduce them into a mindset that explains their grievances to them.
"And in the case of Islamism extremism at its worst, it gives them theological permission to murder innocent people."
Prof Acheson said one of his 2016 recommendations, which was partially implemented, was the creation of separation units for isolating the most subversive terrorists who were intent on grooming other prisoners.
He added: "Obviously the problem extends beyond that but I have no idea whether or not yesterday's offender (Amman) was trying to spread his hateful ideology or he may have just have kept it intact when he was inside.
"But that is part of the problem. I think that we are failing to assertively and robustly manage the threat inside prison and too often because of the general instability and disorder inside many of our prisons, people who keep their heads down are simply left alone. And we cannot go on like that."
He said that in many cases prisoners who didn't cause problems took the first opportunity they got when they were released to try to murder innocent people.
Prof Acheson said many ordinary people looking at the system that released Amman were rightly baffled. He added: "We need a root and branch change in the way we manage this risk."
In his 2016 review, Prof Acheson recommended that the recruitment, selection, deployment and supervision of Imams to work with Islamist prisoners needed to be revamped.
We are faced again with the mystery of a young man who thinks he is doing God's work by stabbing strangers in the street. Sudesh Amman was motivated by a theology which says that these people are infidels worthy only of death.