LONDON — Britain’s most dangerous extremists will be locked up in isolated high-security prisons within prisons to prevent them from radicalising other inmates, the government has announced.

The overhaul of the British prison system came just days after it was revealed that hate preacher Anjem Choudary had been convicted of swearing allegiance to Islamic State (IS) and faced a decade behind bars, prompting concerns that he could recruit other inmates.

The new units will be built inside some of the United Kingdom’s highest-security jails and house the most extreme inmates who promote terror and violence.

They will be kept away from other inmates to end the practice of radicalisation in facilities around the UK, allowing preachers to spread their message to vulnerable young men.

Although the units will be sealed off from the main prison, extremists will not be isolated from each other, ministers have admitted. Measures would be put in place to manage the inmates’ ability to plot together, a source confirmed, after concerns were raised that the units could help extremists form bigger networks within the UK.

Announcing the plan, which is being revealed ahead of a full strategy to tackle radicalisation in British prisons this week, the Justice Secretary, Ms Liz Truss, said the inmates would receive targeted treatment.

“The rise of Islamist extremism poses an existential threat to our society. I am committed to confronting and countering the spread of this poisonous ideology behind bars.

“Preventing the most dangerous extremists from radicalising other prisoners is essential to the safe running of our prisons and fundamental to public protection,” she said.

The specialist units are expected to be built in up to eight high-security prisons in the UK and each is likely to hold fewer than 50 inmates. They form part of a large-scale prison review project undertaken by Mr Ian Acheson, a former prison governor, under former Justice Secretary Mr Michael Gove, which aimed to halt radicalisation in the UK.

Mr Acheson told a parliamentary committee hearing in July that there was a “significant fear among prison staff” about confronting Islamist ideology within prisons and that staff training was poor and patchy.

There are around 130 convicted Islamist terrorists in UK jails, figures suggest, and many more are thought to have been influenced by hate speech and preaching inside jails.

Currently, prisoners who could influence others to pursue terrorism are dispersed within the prison system and moved around to prevent them from forming links with other groups.

Mr Acheson’s review also calls for new measures to halt extremist literature and sermons within prisons and demands better training for staff. Government measures to tackle extremism will be announced this week.