I’ve heard one motor manufacturer claiming 140mpg for a plug-in hybrid with a range of 20 miles or so on its electric motor. The petrol engine produces 40mpg. Therefore you could conclude that if you used all the stored electricity then drove a further eight miles on petrol you would have covered 28 miles on one-fifth of a gallon, hence 140mpg. But how often is a company car driver going to do that?

I guess that if your drivers’ journeys are short, with recharging time and facilities at both ends, then the figure is not inaccurate. But I suspect that most fleets who take a plug-in hybrid on the basis of potential fuel consumption alone are going to be disappointed when the true cost is calculated.