I had a crack at it. The "light jam" technique did not work. I could see it moving the lens elements as I turned it, but no release! I ventured to Step 3 (removing the small black cover) but a) I lost my bottle and b) I don't have screwdrivers small enough for one of the screws. I feared I was going to make it worse.
I have asked my friend RJ (lives in Jersey, used to frequent APUG) if he has ever had this problem and if he would have a go at it for me. If not, then I guess it's £250+ to have Hasselblad Repair do it for me (unless anyone in or near Derbyshire want to do it for me for a little pocket money?!) :-(
Thanks for all the links and useful tips gents.