Driving style (how hard you accelerate and brake)
air con running
windows open
roof box/bars
weather
type/condition of roads possibly
hills! If your driving at 70 on a downhill section of motorway will be using less fuel than do the same going up hill!
Quality of fuel - I have noticed recently less MPG on morrisons (cheapest until yesterday) against Tesco fuel. However, the Shell garage around the corner has dropped to 97.9


