After the fight in the canteen Danny was dragged away by the guards, seen wearing laceless shoes. But in solitary he is seen wearing sneakers with laces, something that would not be approved in such a place.
Monk is described as having killed over 20 people, which would make him one of the UK's most prolific serial killers. At the start of the movie, Longmarsh prison is described as a Category B prison. Monk would almost certainly be deemed a high risk Category A restricted status prisoner, and would be imprisoned somewhere like HMP Belmarsh.