Yes, Mk2's aren't fully OBDII compliant. You need a Sykes Pickavant or a Rover TU4 to eliminate some of the codes. I have been able to reset a few with my ELM327, but not all.
ANY warning light that won't go out on your dashboard means instant fail these days, so best to avoid lighting 'em up in the first place!
Digimafams available here:
http://tuning-diesels.com/Mafam/maproject.htm