Spymaster
Plastic Paddy
You'd think there would be some sort of controls around that.
There are. Huge ones. This sounds like either bollocks or embellishment.
I've been through Broadmoor several times (used to play cricket against the inmates once a year in the 80s).
There's massive security all the way through, electronic gates in all the corridors where you get locked into holding areas and the front gates don't open until the back ones have locked, other internal gates that are manned etc, etc,.
Certainly not somewhere that a person could "have the keys to".
Broadmoor's always been very secure. The odd escapes that happened in the 70s and 80s were invariably someone doing a runner whilst on an outside visit of some sort.