His Majesty's Prison Belmarsh is a Category-A men's prison in Thamesmead, south-east London, England. The prison is used in high-profile cases, particularly those concerning national security. Within the prison grounds is the High Security Unit (HSU); this has 48 single cells and is regarded as the most secure prison unit in the United Kingdom. It is run by His Majesty's Prison Service. History Belmarsh Prison was built on part of the East site of the former Royal Arsenal in Woolwich, and became operational on 2 April 1991. It is adjacent to and adjoins Woolwich Crown Court. 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". The law lords later ruled in A v Secretary of State for the Home Dept that such imprisonment was discriminatory and against the Human Rights Act. It is often used for the detention of prisoners for terrorist related offences. In September 2006, the number of such prisoners was 51. In May 2007, there was a violent disturbance in the prison, Sky News reported. At least four prison officers were injured. In 2009, an archaeological dig on site led to the discovery of a 6,000-year-old trackway in the prison, the second oldest known wooden trackway in Northern Europe after the Sweet Track near Glastonbury. In November 2009, an inspection report from the Chief Inspector of Prisons criticised the "extremely high" amount of force used to control inmates at the prison. The report also stated that an unusually high number of prisoners had reported being intimidated or victimised by staff at Belmarsh. In 2010, HMP Isis Young Offenders Institution was opened within the perimeter wall of Belmarsh Prison. The prison today Belmarsh is a Category A Prison holding prisoners from all over the United Kingdom. In addition, Belmarsh is a local prison accepting different categories of prisoners from primarily the Central Criminal Court (Old Bailey) and Magistrates' Courts in South East London. It also serves Crown and Magistrates' Courts in South West Essex. Accommodation at the prison is a mixture of approximately 60% multi-occupancy cells and 40% single cells, distributed mainly across four residential units. Inmates at Belmarsh are offered access to education, workshops and two gyms. One gym focuses on