Found this on the Esso website:
“What’s in our Synergy Supreme+ 99 premium petrol
Our Synergy Supreme+ 99 petrol has more cleaning power than our regular petrol – and includes molecules whose job it is to reduce the friction in your engine helping the moving parts work more efficiently.*
Although our pumps have E5 labels on them, our Synergy Supreme+ 99 is actually ethanol free (except, due to technical supply reasons, in Devon, Cornwall, North Wales, North England and Scotland). Legislation requires us to place these E5 labels on pumps that dispense unleaded petrol with ‘up to 5% ethanol’, including those that contain no ethanol, which is why we display them on our Synergy Supreme+ 99 pumps.
There’s currently no requirement for renewable fuel, like ethanol, to be present in super unleaded petrol although this could change in the future, in which case we would comply with any new legislation.”
I think I need to flush through my tank of E10!
(Thanks for all the responses to my post - Its really good to know there is so much support and experience out there 🙂 )