I purchased a four-month old Venture edition Mazda MX-5 with 1050 miles on clock. Test drive was okay a week before. After buying car (empty fuel directed to shell garage down road) Filled up with Unleaded - but after 30 miles on the trip home, the engine warning light came on.

Was advised by dealer to stop driving and take it to nearest Mazda specialist dealer for assessment. They spent four hours testing all computer codes, and ended up charging me £404 to drain all fuel out of tank - claiming it was a 'historic fuel problem'. The knock sensors were reset - but I now feel like I have been left out in wind!

Complained to original dealer as well as Shell. No Joy. I've kept the drained fuel, but independent testing costs £800+. So who do I complain to who now? First tank of petrol I put in (I kept receipt), and it was not wrong fuel! No one wants to know, hope you can advise...