The number of individuals incarcerated for terrorism-related offences in Britain has reached a record high, according to government data released this week. As of the end of March, there were 273 prisoners held on terror charges, marking an increase of seven compared with the previous year and more than doubling the figure recorded when official records began in 2010.

Among those imprisoned, 58 percent (159 inmates) were identified as holding Islamist extremist beliefs, while 29 percent (80 prisoners) subscribed to far-right extremist ideologies. The remainder, 34 inmates, were associated with other forms of extremism, including left-wing radicalism. Religious affiliation data indicates that 60 percent of these offenders self-identified as Muslim, while 20 percent identified as Christian.

The majority of terror offenders in custody—80 percent or 219 individuals—declared the United Kingdom as their country of origin. Other nationalities represented include eight prisoners from Iraq and five from Iran.

The statistics also reveal that 41 terror-related offenders were released over the past year. Under current government policies, which have been temporarily suspended, terrorists are excluded from early release provisions intended to alleviate prison overcrowding. These individuals are required to serve a minimum of two-thirds of their sentence.

Additionally, there has been a notable rise in terrorism-related arrests linked to the proscription of the activist group Palestine Action. Of the 3,061 arrests for suspected terrorist activity in the year leading up to March, 2,819 were connected to alleged support for the group following its ban in July 2025.

These figures illustrate ongoing challenges for the British criminal justice and security systems in addressing the evolving landscape of domestic extremism.