the categorisation of most secure prisons, thus the category for highly dangerous prisoners or those considered most likely to escape. 'Cat B,' 'Cat C', and 'Cat D' are also used in decreasing order of required security. These categories have been in force since 1966 UK, 1996

to categorise a prisoner as Cat A. 'Cat B', 'Cat C' and 'Cat D' are also used in decreasing order of required security. UK, 1996