Well, I am about to be charged £150 plus to have the O2 sensor on my Megane replaced. The fault was explained to me as having been caused by generally poor petrol in the South East at the moment! Especially from the supermarket chains. I have been advised to only use the higher octane more expensive petrol such as Optimax. So it would seem petrol is not petrol is not petrol!
There's big noises being made about this at the moment.
BBC NEWS | UK | Inquiry into 'contaminated' fuel
I must admit that the Porker only gets to dine on Shell V -Power (previously Optimax), I would put virtually anything in the Grandis but it tends to be 'main brand' BP/Shell etc rather than Supermarkets because they are the convenient garages near us.