Hello!
avionimc: I strongly disagree...
Over the years, I have encountered two self-taught IFR pilots who perished whilst perfoming their act. One sadly took his girlfriend and two small children with him, the other had "only" one passenger aboard. But I cannot derive any statistics from that, because I do not know how many self-taught IFR pilots survived the experience...
And to Miroku: I understand your motivation now and that you want to get tuition by an instructor. Which is a good thing in a way. I know nothing about the UK NPPL, but as a JAA IFR instructor, I am not allowed to train anybody in instrument flying outside an official course. If I did anyway, it would be without insurance cover and with the risk of losing my licence in the process. So before beginning the training, I would strongly recommend to check the legality of the whole plan.
Happy landings,
max