Belmarsh Prison is a high security prison in London, England. Operational since 2 April 1991, the facility can hold 921 inmates. It has been used to detain a number of people indefinitely without trial under the provisions of the Anti-terrorism, Crime and Security Act 2001. Doctors and human rights groups have raised serious concerns about the mental and physical health of these prisoners.

The politician and writer Jeffrey Archer began his prison sentence in Belmarsh when he was convicted of perjury in July 2001, though he was moved to the category C Wayland Prison after only a few weeks. The controversial preacher Abu Hamza is currently an inmate.