It requires persistence to visit Al Evans. After you have surrendered your passport, declared any explosives and locked your mobile you must wait for the next openings of two sets of electronic doors. Then it's a quarter of a mile of concrete corridors, some inside between locked steel gates and some across the grounds, caged in metal. "I've overdosed on Night Nurse," says the drugs counsellor when I reach her, "so I'm sorry if I'm a bit out of it!"

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