Just to add to the debate about the 500 TwinAir, my daughter has been running one in London for a year now, and has done 5000 miles. Average fuel consumption is 33.3mpg according to the computer - and she drives with the eco button on all the time. I have had a Volvo XC60 D5 205ps Geartronic, which is fantastic, for two years; 30,000 miles and average 33.2mpg. Weird, isn't it?