My God, what have I started! I only asked for suggestions for books/DVDs which could help me whilst I did some instrument training with an instructor. By the way, he is a former RAF instructor, current 747 pilot and also teaches PPL, IMC, aerobatic and formation flying.
Having now learnt a good deal more about the subject and read the more apposite comments it would seem that my basic idea to gain experience of instrument flying was a good one.
However, it is all very well to say that I should never put myself in the position of flying in cloud. Many more experienced pilots than myself have been caught out unawares. Having read the letters in AOPA magazine, a lot of pilots expressed the view that their ability to fly on instruments saved their lives and this is where I am coming from.
Regarding the update of an NPPL to a PPL this is not possible in my case due to medical reasons. I believe it it this reason, rather than cost, that most people opt for the NPPL.