Fuel

kentman

My 1963 Mark X Jaguar has recently had running problems due to the ethanol in 95 octane fuel.  Also, in France this summer, my Freelander 2 suffered rough running after a couple of fills of supermarket diesel but returned to smooth running after refilling
with a premium brand.  I have now been advised by specialists in both models to avoid supermarket fuels.  Do any members have the technical knowledge to advise whether we should all be using only premium brands of fuel?