Haven't added to the poll as I have a convertible (heavier than a normal ONE

) but I used to average around 30mpg using normal 95RON unleaded. I tend to get 2-3 mpg more using super unleaded (loving the Tesco 99)
That's mostly 'enthusiastic' around town (not city centre) driving. Can get a lot more if I really try but who wants to coast around at 1500rpm?
