David,
Thanks for your reply.
The number is definitely B41048...,the only small doubt is about the last number(on the frame at least)which seems to be a 3,although there looks like the letter z superimposed.The same number,with the prefix M appears on the motor,although I don't have it here with me at the moment to confirm any possible questionable marking,and on the log book.
Your idea of photos seems a good one,I will try and sort that out,but I'm a relative novice on the computer front,so I"ll seek advice on that too. Thanks again Chris