Attack on officers raises questions about separation centres at jails in England

HMP Frankland, near Durham, is a category A maximum security jail with more than 800 inmates. Photograph: Tom Wilkinson/PA

With its high, ugly, grey concrete perimeter walls HMP Frankland looks as grim from the outside as you would expect for a place nicknamed “Monster Mansion”.

Since it was opened in 1983 on the leafy outskirts of Durham – near a 13th-century priory used for centuries as a holiday retreat for Benedictine monks – its inmates have included Peter Sutcliffe, Harold Shipman and Charles Bronson.