HMP/YOI Isis is in South East London and is the first bespoke establishment of its kind in the London region, being a young adult and category C training prison for young men and adults up to the age of 30. The prison was constructed within the perimeter of HMP Belmarsh and received its first prisoners on 26 July 2010. Isis is the first whole-build public sector prison to be built in the last 20 years. In December 2016, the age cap of 18–30 was lifted, allowing prisoners of all ages to be transferred to Isis
The two house blocks, Thames and Meridian, both have with four spurs radiatingfrom a central hub with three landings on each spur. On average there is accommodation for about 80 prisoners on each spur in a mixture of single and double cells. There are also a few fully-equipped cells for prisoners with disabilities.