If your 3 series is late teens, then you’ll have no issues using E10 when it comes to MOT time imo.CO - 3series/i6, late teens.
just reading this https://bmwcarclubgb.uk/docs/e10-ethanol-in-petrol-for-bmws/
“One other thing to look out for is hot-running. Ethanol actually burns at a lower temperature than petrol. If you look at the molecular structures of petrol and ethanol, you will see a major difference: ethanol contains an oxygen atom, whereas petrol is oxygen-free. When the ethanol petrol blend is combusted in the engine, the oxygen supplied by ethanol – that would not be there in pure petrol – is now added. This causes the fuel-air mixture to become leaner and can result in hot running. However, it can be resolved by setting your fuel mixture slightly richer.”
... so e10 could warm up cat faster
I'll go out and try and burn remaining E10 tomorrow,
The issues arise on much much older cars that aren’t designed to use it.
I MOT full time and haven’t heard of or experienced any cars failing due to E10 use (not to say it isn’t possible) and if they do fail on CO, it’s always another reason.