The RAC website says:
The consequence of putting E10 fuel in an incompatible vehicle depends on the vehicle/engine variant and how much fuel has been put in.
It may cause some pre-detonation (‘pinking’), and perhaps a little rough running and poor cold starting, but it shouldn't be a disaster for the driver.
Simply top up with the correct fuel suitable for the vehicle as soon as possible when around a third to half the tank is used.
There has also been discussion in Historic vehicle circles about Ethanol for quite a while. The Federation of British Historic Vehicle Clubs has an interesting page about this https://www.fbhvc.co.uk/fuels , the main issue is that the fuel line components in many older Historic vehicles aren't compatible with Ethanol, but replacing older flexible fuel pipes with modern materials generally addresses this. The main issue for Historic vehicles will be fuel degradation of stored fuel, and increased risk of vaporisation and fuel locking where fuel lines get hot. i've seen posts elsewhere of this being addressed by installing heat shields or re-routing pipework and using the car more often!