Next Potteries branch meeting: Monday 19th Jan.
See:
http://potteries.mmoc.org.uk/Contact.htm
I seriously doubt that the fuel would have caused the head gasket to go, like has been said, the valves (especially exhaust valves) would go first.
I think Cam could and should open a moggie service centre
I would love to, but I don't think there is the demand in our area or the money in it for me to give up my current job! Plus it would be rather unpleasant in winter!!!
For fuel and additives, use either normal unleaded or shell optimax PLUS a good fuel additive.
I use Castrol Valvemaster plus (available from Halfords at £9.99 a bottle) which treats 250 litres (or 10 tanks full).
p.s. Nick, have you got some photos of your car?? if so can you bring them along to the next meeting for me to scan and bring a little write-up on your car, so I can put them on our website (that is if you are wanting to become a member!!):
http://potteries.mmoc.org.uk