Instrument Flying stuff
Hi Miroku,
The standard texts on the subject are the Trevor Thom books, the Jeppesen Sanderson one covers it in great depth albeit from an American perspective. My favorite is the Instrument Flight Training Manual written by Peter Dogan and developed by Professional Instrument Courses Inc. The latter book is relatively concise and includes 'war stories' to illustrate each section. I found this book useful when doing the FAA IR in 1997.
You mention that you fly on an NPPL, so I assume you are doing the instrument training out of general interest, rather than a desire to hammer off in to hard IMC and fly airways. This is an excellent idea, as good instruction of any kind is worth having. Most people recon that instrument training improves the accuracy of their VFR flying.
As you are probably aware, there are two aspects to instrument flying. The first is controlling the aircraft by sole reference to the instruments. This includes identifying instrument failures and flying on 'partial panel'.
The second or applied part of the training involves the navigational aspect of instrument flying. This includes navigation by VOR, NDB, GPS and ILS etc. It also includes things you need to know to conform to the IFR system, like holds, SIDs, STARSs, Lost Comms Procedures etc. Many of the books and electronic media devote a lot of time and material to the applied part of instrument flying, which may be of less interest to you.
Good luck with your flying. I've a selection of books and VHS videos on instrument flying, which although a bit dated (i.e. 1997 - so not much on GPS), may be of use. If you'd like to borrow them drop me a PM.
Safe Flying,
Richard W.