First, the "contamination" bogey.
This is more a figment of imagination, than reality
Yes there was a Supermarket chain that had a batch of"contaminated" fuel.....but that's the only one I know of in over 50 years....I'd venture that deliveries to filling stations will probably be of the order of 100:1 compared to GA._ in terms of volume, it's probably vastly bigger.
Have you bought a fuel-dispensing pump recently?....No, thought not
An operator has to have the pump regularly checked and calibrated -woe betide anyone caught giving wrong measure (the tolerance allowed is ~a teaspoonful per Imp. Gallon) So, nobody will willingly compromise their expensive dispense equipment, which has built in filtration and water-seperators, to protect the metering-head..
UK road-fuel is mandated by law , to have (IIRC) 5% Ethanol...this is the maximum that legacy fuel-systems will reliably tolerate. As with the Lead-free furore, there would be major problems converting the nation's cars to accept higher Ethanol content and given that MPG suffers, any advantage is political,rather than practical.
I'm sure tha vast majority of UK GA activities could quite happily continue on standard Pump Petrol with no percieved difference....Aerobatting on a hot day, might be an exception...that, I don't know. Certain designs, with valve-seats cut straight into cast-iron heads (and some valve-guides too!) relied on the Lead, to coat and lubricate the working surfaces...Aeroengines with hardened seats do not have this problem.. Once you get a petrol-engine warm, it'll run on paraffin.....smokey and lower power, but it'll run Morris Vedette marine engine was built that way, as were many petrol/TVO tractors
That shows that petrol-engines are very robust and very tolerant of fuel-quality PROVIDED THEY ARE MANAGED CORRECTLY.