The highest category of prison in the UK penal system, prisoners kept in these facilities are categorised as among the most dangerous in the system. This includes prisoners found guilty of such crimes as murder, rape, indecent assault, armed robbery, terrorism and the supply or use of explosives. Category A prisons often enjoy local notoriety - particularly as many retain a fearsome outwardly Victorian aspect. Armley Prison in Leeds, for example, looms menacingly over the South Westerly quarter of the city, its bleak exterior resembling nothing so much as a medieval keep.
The primary aim of such prisons is to ensure that it is impossible for inmates to escape.