Following the suggestion above I took a look at the No.1 AIDU website (
www.aidu.co.uk). Sadly it seems that although at the moment you can buy IAPs in books and individually cheaper here than anywhere else, this is all about to change. They are gradually replacing the existing charts with AERAD ones; and AERAD won't allow them to be sold on to civilians. I guess that's the creeping outsourcing of the armed forces again.
I'm going to try to persuade them that I am military personnel for the purpose of this ruling...!
Plt Off T. M. Morris RAFVR(T) (i.e. a noddy officer in my school's Cadet Force!)