Around 78,000 people are in prisons in the UK at the moment. They are looked after by about 49,000 staff in 153 prisons.
Who are Category A prisoners?
Adult men in prison are put into groups depending on the crime they were found guilty of and how dangerous they would be to the public if they escaped. There are four of these groups which are called security categories.
Category A: The most dangerous prisoners. If they escaped there would be a huge threat to the public. The prison service aims to make it impossible for these people to escape.
Category B: Less of a threat to the public, but still dangerous enough to need levels of security which make it very difficult for them to escape.
Category C: Prisoners who are thought to be of very little threat to the public, they either don't want to escape or don't have the skills needed.
Category D: People who do not pose a risk to the public and are unlikely to escape. These prisoners can be held in open prisons.
Women prisoners and young offenders (anyone aged between 15 to 21) are not categorised like adult male offenders.