Technically, petrol in the UK (and wider Europe) is sold meeting a single standard (EN 228) which defines two distinct fuel types, but confusingly these don't relate to octane, which is how fuels are commonly differentiated at the retail pump, but by ethanol content.
Fuel with 10% ethanol, E10, is designed for all modern vehicles, with 5% ethanol being
intended for older vehicles which may have issues with the higher ethanol blend. It is assumed that for all but really old classics E5 is benign, but this is debated in some quarters.
In practice, in much of Europe that means that ‘super premium’ 97+ RON products are going to be E5 and the ‘normal’ stuff will be E10, but you will see countries where this varies.
Your car will run fine on any fuel, but obviously higher resistance to knock is desirable. This means higher octane.
Now consider that ethanol itself has a very high octane rating, something like 109 RON iirc, and think what that means for quality of the other 90% in a 95 RON E10 mix…
Ethanol also has a lower calorific value than petrol so there is less energy in it (and therefore less that can be extracted to do work), which is why the consumption will be higher to get the same performance as
@SckSqzBngBlo says above.
On the positive side, ethanol has a very high latent heat of vaporisation which means it helps keep cylinders cooler during combustion, the main reason high power builds commonly target a high ethanol fuel blend because it allows for more boost.
Complicated stuff, but with the standard ECU and fuel system I’d stick to the highest octane you can get your hands on, and in Europe that will generally be the ‘super premium’ E5 mix.
Personally, I almost always fill up with Aral’s 102 RON which is of course E5.
