I was a bit tired to take a look at this, so only had a play today.
The car runs perfectly when cold, idles nicely, seemed to take off ok. It starts playing up when it's warmed up, and going back to idle shows a very slight misfire (engine sounds fine, I can only hear it from the exhaust) - disconnecting a spark plug produced a much more prounced misfire and a less healthy sounding engine (I tried them all, but each caused a completely different effect to when they're all connected).
I did the ecu diagnostic, by shorting the pins and checking for an error code - there were none stored.
Is there something else I should be looking at here? I would think the difference between hot/cold running would rule out the Distributor and sparks (and I would have thought that'd produce an error code)?