The UK government has announced new plans to “tackle extremism in prisons,” including through the creation of “specialist units” for “the most dangerous Islamist extremists,” and a new “directorate for Security, Order and Counter-Terrorism, responsible for monitoring and dealing with this evolving threat.” 
The government’s proposals are based on a review completed in July 2015, of which only a summary has been published.
The review’s key findings include “evidence that IE [Islamist Extremism] is a growing problem within prisons, and a central, comprehensive and coordinated strategy is required to monitor and counter it,” that there should be “a more coordinated and rehearsed response to violent incidents,” and:
“the present system under which TACT [Terrorism Act 2000] and IE prisoners are dispersed across prisons should be reviewed, and consideration given to containment of known extremists within dedicated specialist units.” 
The government has also published its response to the review, which sets out the plans in more detail. On the issue of “specialist units”, it says:
“Planning is under way to create specialist units within the high security estate to allow greater separation and specialised management of extremists who pose the highest risk to other prisoners.
We are also reviewing options for improving the identification and management of extremist prisoners. Prisoners are categorised and managed according to their risk, and this principle will be maintained.” 
The review was written by Ian Acheson, a former Home Office official, who as part of his investigation:
“visited Maghaberry prison’s Roe House, the ‘prison within a prison’ that holds some of Northern Ireland’s most high-profile terrorists, and prisons in the Netherlands, France and Spain, where jihadi prisoners are segregated.” 
A report published in The Guardian earlier this year highlighted concerns over the use of solitary confinement in prisons in France, the Netherlands and Belgium:
“Prison isolation may not only be inhumane, but also ineffective. Critics say the practice may make people more vulnerable to extremist ideas, and stress that eliminating communication among prisoners is often impossible.” 
 Ministry of Justice press release: Government sets out new measures to tackle extremism in prisons, 22 August 2016 (pdf)
 Summary of the main findings of the review of Islamist extremism in prisons, probation and youth justice, August 2016 (pdf)
 Government response to the review of Islamist extremism in prisons, probation and youth justice, August 2016 (pdf)
 Toby Helm, Extremist prisoners to be isolated in ‘sealed units’, The Guardian, 21 August 2016
 Aviva Stahl, Concern over ‘political’ use of solitary confinement in European prisons, The Guardian, 2 May 2016