A convicted terrorist was eight months into a deradicalisation programme when he tried to murder a prison guard.
Brusthom Ziamani, 25, was jailed for life after he and Baz Hockton, 26, attacked Neil Trundle at HMP Whitemoor in Cambridgeshire in January.
They were armed with makeshift weapons and wore fake suicide belts for the targeted attack.
The Prison Officers Association (POA) has called for a "fundamental review" of deradicalisation schemes.
The assault on Mr Trundle is the first terrorist attack to occur inside a British jail.
Ziamani must serve a minimum 21 years, while Hockton will serve at least 23 years before he is eligible for parole.
Sentencing, Mrs Justice May told Ziamani: "You were eight months into a year-long programme designed to address such beliefs when you committed these offences.
"Your current twisted view of Islam needs to moderate and change. It is not possible, at this stage, to determine for how long you will remain a danger."
Mark Fairhurst, national chairman of the POA, called for a "fundamental review" of prison deradicalisation programmes following the attack at Whitemoor.
"It's not the first time someone who has completed the course or is due to complete the course has committed an atrocity", he said.
Prison deradicalisation schemes have faced increased scrutiny following terrorist attacks by recently released convicted terrorists.
Saskia Jones, 23, and Jack Merritt, 25, were killed by former Whitemoor inmate Usman Khan, 28, in November during an attack at a prisoner rehabilitation programme event near London Bridge.
Khan, who had been released almost a year earlier halfway through a 16-year jail sentence for terror offences, is said to have taken part in both prison deradicalisation schemes.Mr Fairhurst suggested more prisoners should be sent to separation centres, sometimes called "jails within jails".
Only about six inmates are thought currently to be subject to the regime announced in 2017 to tackle extremism in prison.
The only one currently in use in England and Wales is in County Durham's maximum-security Frankland prison, where Manchester Arena bomb plotter, Hashem Abedi, 23, is serving his sentence, although Full Sutton and Woodhill also have them available.