My primary sources are two Prison Officer friends and my brother who worked as a Senior Prison Officer for over 20 years at jails such as Armley and Wakefield and a book called 'Drugs In Prison' by Steve Gravett.
However, the internet is full of it:
www.rt.com/uk/235759-serco-corruption-allegations-drugs/
http://www.ibtimes.co.uk/prisoner-ha...nd-eye-1517658
http://www.theguardian.com/commentis...zero-tolerance
http://www.bbc.co.uk/news/uk-31625243