engine died during trackday - any ideas?

HI

Just been offloaded back home from a recovery lorry. I was at a trackday at Abingdon when the engine cut out at about 6000rpm. Got it going again, a little bit reluctantly buty seemed ok, then the same thing happened which resulted in the current symptoms of:

if started and left alone, revs drop to ~250rpm and attempts to idle there for a few seconds before stalling

if held on part throttle, will intermittently cut out for a second, get going for a few seconds, cut out for a second etc. at regular intervals.

Would be grateful for any ideas if you have them!

Mk 1 1.8, standard apart from induction kit.