an update on this!
During the MOT had an advisory on the passenger side rear wheel bearing a bit loose. While going about tightening the nut to the bearing I noticed that the nut was completely off and resting on just the split pin.... probably due to the silly heat cycles from the track abuse at combe and would explain the car stepping out a lot at the end of my last session lol.
Anyway tighten the bearing up took it for a good spin one night and the warning light went off then back on and so on..... started it up Saturday to give her a wash and magic! The light stayed off so the car repaired itself, got to love the mk2!
All I can guess is the bearing came loose and the spoigt on the back came away from the abs sensor??? Anyway it's all fine now and I'm happy.