Right. Finally sorted it. In case others have a similar problem, here's what I did.
Originally, when I plugged it in (at a friends BMW/European specialist workshop) it came up with misfires on cylinder 3 and 5. I put a tank of 98 in it. It started running better. Made me think it could be a fuel/air issue. Replaced air filter. No change. Then I checked the DISA and found the typical problem of the shaft was rounded and turning in the housing. Fixed that and it ran even better. Now with just a slight miss when accelerating of the mark. Plugged it in again. 3 and 5 are fine but cylinder 2 now missing.
Cleared the codes. Ran the car for a week to let timing adjust. When the tank was empty, I put 95 back in and still the same. Plugged in again and cylinder 2 still coding as a misfire. Changed the coil pack and viola! Fixed! Ended up being a combination of those things. Funny how the computer at BMW couldn't diagnose all at once but, I got there in the end.