Then they nip down to the supermarket and put in the cheapest and nastiest stuff possible. No thanks, for the sake of £50 I'd rather full it up myself and know from the outset the engine is getting the best start to life.
Makes no odds to me - there is no proof that more expensive fuel provides better performance and prolongs engine life. I've been using supermarket fuels in my Mk5 GTI for years, and it has been as reliable and consistent as ever. Make sure you drain what is in your tank first though, don't want that premium stuff getting contaminated!
you sure about that 
http://www.autocar.co.uk/car-news/motoring/high-octane-equals-better-mpg
Interesting...
The Astra VXR; does Vauxhall recommend 98 RON?
The point is, it depends on what the car is mapped for, if it is mapped for 95 RON putting a higher octane rating should not give you more power, or better fuel consumption.
If you put 95 RON in a car mapped for 98, I would expect to see what Autocar found... the car backs off the timing to avoid detonation (pinking) and the less optimum settings result in less power and greater fuel consumption...
So, if the Golf is mapped at the factory for 95 RON, putting 97, 98 or 99 in should make no significant difference...
