HM Prison Belmarsh is a Category A

Prison security categories in the United Kingdom

There are four prisoner security categories in the United Kingdom used to classify every adult prisoner for the purposes of assigning them to a prison. The categories are based upon the severity of the crime and the risk posed should the person escape....

 men's prison

Prison

A prison is a place in which people are physically confined and, usually, deprived of a range of personal freedoms. Imprisonment or incarceration is a legal penalty that may be imposed by the state for the commission of a crime...

, located in the Thamesmead

Thamesmead

Thamesmead is a district of south-east London, England, located in the London Boroughs of Greenwich and Bexley. It is situated east of Charing Cross....

 area of the London Borough of Greenwich

London Borough of Greenwich

The London Borough of Greenwich is an Inner London borough in south-east London, England. Taking its name from the historic town of Greenwich, the present borough was formed in 1965 by the amalgamation of the former area of the Metropolitan Borough of Greenwich with part of the Metropolitan...

, in south-east

South London

South London is the southern part of London, England, United Kingdom.According to the 2011 official Boundary Commission for England definition, South London includes the London boroughs of Bexley, Bromley, Croydon, Greenwich, Kingston, Lambeth, Lewisham, Merton, Southwark, Sutton and...

 London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. Belmarsh Prison is operated by Her Majesty's Prison Service

Her Majesty's Prison Service

Her Majesty's Prison Service is a part of the National Offender Management Service of the Government of the United Kingdom tasked with managing most of the prisons within England and Wales...

. Isis Prison

Isis (HM Prison)

HM Prison Isis is a Category C male Young Offenders Institution, located in the Thamesmead area of the London Borough of Greenwich, in south-east London, England...

 is a Young Offenders Institution which is sited within the perimeter wall of Belmarsh Prison.
Belmarsh Prison was built on part of the East site of the former Royal Arsenal

Royal Arsenal

The Royal Arsenal, Woolwich, originally known as the Woolwich Warren, carried out armaments manufacture, ammunition proofing and explosives research for the British armed forces. It was sited on the south bank of the River Thames in Woolwich in south-east London, England.-Early history:The Warren...

 in Woolwich

Woolwich

Woolwich is a district in south London, England, located in the London Borough of Greenwich. The area is identified in the London Plan as one of 35 major centres in Greater London.Woolwich formed part of Kent until 1889 when the County of London was created...

, and became operational on 2 April 1991. Belmarsh is adjacent/adjoined to Woolwich Crown Court

Woolwich Crown Court

Woolwich Crown Court, located at 2 Belmarsh Road, Thamesmead is one of twelve Crown Courts serving Greater London.It stands adjacent to both HM Prison Belmarsh and Belmarsh Magistrate's Court. Operational from 1993, it has 7 courtrooms and deals with more than 750 cases a year. Until recently,...

, which means the prison can be used for high profile cases (including those concerning national security).

Between 2001 and 2002 Belmarsh Prison was used to detain a number of people indefinitely without charge or trial under the provisions of the Part 4 of the Anti-terrorism, Crime and Security Act 2001, leading it to be called the "British version of Guantanamo Bay".