most elderly vehicles can stand E5(5%ethanol) but are likely to be affected long term by E10.

The old (80 - 130 years) I work with are badly affected by E5. Fortunately, we have a supply of avgas (ethanol free) - I wonder why avgas is ethanol free?

Avgas is ethanol free because fuel containing ethanol is not approved for use in aircraft by the UK Civil Aviation Authority. It attracts moisture from the atmosphere, and the last thing you need on an aircraft is water in the fuel.

He also tried Avgas some years ago for a bit of extra go on track days. Took it to his local rolling road and was shocked to find it produced less power than on supermarket pump petrol a few months before. I don't know the exact science but the chap explained that it was a mistake many customers used to make years ago, apparently avgas is designed to burn slower in lower revving aero engines to produce the power. Put it in a high revving, tuned road engine and it simply does not work.

Avgas is available in low octane unleaded and high octane 'low' lead. Higher octane doesn't mean more power, it burns slower to take advantage of higher compression ratios without pre-detonation. Both have the same calorific value.

We have had UL 95-E10 for some time in france, I only run petrol in motorcycles and various chainsaws, dumper, mowers etc and avoid E10 because of the hygroscopic problem and general running problems.

As soon as it becomes clear that I have done the last mow of autumn, I empty the mower of petrol and add it to my car .... Haven't had a fuel-related problem so far. In fact it hasn't been serviced for a couple of years as it may come back worse than it went in. All I have done this winter is to clean the plug.