Answer
During the summer of 2021, the standard (or premium) grade of petrol in the UK will become E10, meaning that the petrol contains up to 10% renewable ethanol – this has been done to reduce carbon dioxide emissions and help tackle climate change.
E10 petrol can be used in almost 95% of petrol powered vehicles on the road today, including cars built since 2011. You can check whether your vehicle is compatible with E10 petrol here.
If you can't use E10 petrol in your vehicle, you will still be able to use E5 petrol by purchasing the 'Super' grade petrol available at most petrol stations.
Petrol stations will clearly label E10 and E5 petrol using these markings:
Note that the change only applies to petrol – diesel fuel remains unchanged.
Providing your vehicle is compatible with E10 petrol, there's no reason you can't mix the two grades of petrol (E5 and E10). It's perfectly safe to mix them in the same tank or fill up with E5 if E10 is not available.
If you put E10 petrol in a non-compatible vehicle, simply fill up with E5 ('Super') petrol next time. Using a single tank of E10 fuel in a vehicle that is not compatible should not be a major problem – just make sure you fill up with the correct E5 petrol next time you refuel. Unlike putting petrol into a diesel engine, you shouldn't need to drain the tank and, on a one-time basis, will not suffer engine damage as a result. However, prolonged use of E10 petrol in a non-compatible vehicle may cause harm and is not recommended.