It's rare that real world driving lives up to manufacturer claims, but that's down to the EU style of mandatory fuel consumption tests, rather than manufacturers trying to fool us, but that shouldn't stop us trying to match them.
Driving a 1 litre Seat Mii through to Edinburgh the other night along the M8 and Edinburgh bypass to the Little Chef at Dreghorn for a business meeting (such glamour, eh?), the wee 3 cylinder motor was returning 63 mpg.
On the way back home along the same motorway route with minimal off-motorway driving, the car was returning 44 mpg, nearly 20 mpg of a difference.
That was entirely down to the style of driving. On the way through during the evening rush hour, the wee car was cruising at never more than 60 mph. On the way home in the deserted darkness, it was cruising at never more than 75 mph (honest officer).
That 12-15 mile an hour difference accounted for damn close to a third of the fuel consumption.