I've done it, I've done it, I've done it!
Sorry, it's just that after weeks of trying, to a complete DIY amateur I'm feeling a large sense of achievement today!
Anyway for any amateurs that haven't attempted it so far my observations are as follows:
1) The vents are a pig to get out, best advice I found was to hold the two clips down with credit cards, then pull vents out (even then I needed to prise the vents out with a knife, carefully I might add)
2) If you have the piano trim, be careful not to scratch it when removing the stereo as I did

(luckily it was minor, looks like a 1/2 inch white hair on the bottom edge.)
3) I bought the kit from BMW (a good excuse for a drive to Hindhead!) £40, and it fitted into the back of the stereo v easily.
4) I haven't drilled a hole in the plate underneath yet, the aux to ipod wire can escape from the side with the plate secured back in for those who don't want to/can't drill the hole needed.
Thanks for all the help given on the many threads on the subject, I can say that the sound quality is excellent and well worth the effort
