He will indoctrinate prisoners in Islamic radicalism - his danger to British society will not change, in fact he may have a bigger and more lethal audience now.
***He will indoctrinate prisoners in Islamic radicalism***
Put him in Solitary, then force him to listen to the Bible on tape, in Arabic or his normal language over and over again for ten years.
Deprogram him from islam.
The only other method of reform I can think of is hang him, dip him in tar, hang him in a cage from a pier like the Brits did Captain Kidd.