Audi Germany advised me that my C3 'should' be OK to use E10, assuming it was all original. Not an answer that filled me with confidence so I will use super as long as it remains E5 and I can get it. The extra cost is negligible in view of how little I use the car and the potential damage.
So far there is one Jet petrol station nearby that sells Super. The official publicity suggested that petrol stations with a high turnover would be required to have at least one pump offering Super, but I'm not sure every retailer will follow that. My two nearest Sainsbury's stations converted to E10 weeks ago but only one has a Super pump.
My daily driver is an E46 and BMW says E10 is safe to use in all their vehicles, regardless of year of manufacturer, so I will chance E10. Nevertheless, I rarely fill up more than once a month, so I hope I won't need to use fuel stabilizers. If I do I hear the FBHVC recommends those made by Millers Oils.
I guess time will tell us more. Most drivers have no idea of E10 or care about its implications. If they find themselves having to spend more though, then that may change...