Thanks Tabetha. Not done anything with it yet, too late after work and its been raining most of today!
I've been out in it tonight and it was "doing it's tricks" and running a bit rough. I had a look under the bonnet in the dark in case there was a firework display anywhere around the coilpack, nothing. I suppose if its breaking down internally there won't be any sparks to see.
Anyway, when (if ) I find the problem I will report back.

Rob.