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Violent extremist prisoners could be held in separate special units inside jails under government plans to stop other inmates being radicalised.

Justice Secretary Liz Truss will reveal the new measures on Monday, following a review into extremism in prisons led by former prison governor Ian Acheson.

One of his key recommendations was to "incapacitate" violent extremists by keeping them away from other prisoners.

His report will only be published in summary for security reasons.

But it is understood to be critical of the current system in which extremist inmates are dispersed across eight high-security prisons.

Last month, Mr Acheson told the Commons justice select committee there was a small of number of prisoners who needed to be kept apart from other inmates because their "pernicious ideology" could be "magnified inside prison, particularly when you have a supply of young, impulsive and often highly violent men".

The publication of the report by the senior civil servant comes only a few days after it was revealed that radical cleric Anjem Choudary had been convicted of inviting others to support the so-called Islamic State.

Fears have been voiced that Choudary, who is due to be sentenced in September, would be able to influence other inmates with his views.

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Ms Truss is expected to accept the separation proposal and BBC home affairs correspondent Daniel Sandford told the News Channel: "This is the policy that pre-dates the Islamist extremist era before 9/11 when we had IRA prisoners in British prisons.

"They were allowed to be mixed in the general population of the high security estate. No-one has really changed that policy in the light of the massive numbers of convictions there have been in the last 15 years since 9/11.

"It's clearly going to be more expensive. There are eight high-security prisons in England and Wales and if you are going to need to have a unit in all or at least some of those, that's going to be an extra cost.

"You're going to have to have separate feeding systems, separate exercising regimes, separate ways of working, separate education systems so it's not that easy."

Ms Truss is likely to announce other measures to clamp down on radicalisation inside prisons.

She said: "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."

The idea of having a separate prison within a prison is not new - similar recent changes have been made in France, while prisoners were also separated in Northern Ireland's Maze prison in the 1980s.