Along with most others in the car industry I’ve long had issues with the way that official EU economy figures are achieved, and the Chevrolet Volt that I drove recently only serves to prove how misleading they can be. According to the confirmed figures, GM’s petrol-electric range extender powertrain allows the Volt to return 235mpg. You know, I know and Chevrolet knows that this isn’t the case.

This figure was reached because the official combined test covers only 100km, and therefore the Volt ran for 80km of those (or we managed just over 70km in varied conditions) on electric power alone, and only covered 20km with the 1.4-litre petrol motor running. The petrol used would then have been calculated over 100km rather than 20km.

Now, there’s no denying that technically the Volt did achieve 235mpg for that period of time. But then if the test had conveniently only covered 80km, the Volt could have been the first petrol-powered car in history to  - officially, at least - use no fuel at all. The 235mpg figure is barely any less misleading. Even a Chevrolet official admitted that dealers wouldn’t be drawing attention to the figure, and would have to explain that it was skewed due to the electric range, for fear of having owners return complaining that their petrol economy is hundreds of mpg less than stated.

A combined figure for what it would achieve with the petrol motor in use over the full 100km would have been more useful as a gauge of what to expect after the electricity had been sucked dry. Provided the Volt’s electric range was also stated that would surely be a clearer forecast for prospective owners. An indication of how much a full recharge of the battery costs (the Volt must be plugged in to recharge) on average, would also be useful.