All but three of the 200 new cars tested by Which? failed to reach their official miles-per-gallon (mpg) figure, with the shortfall averaging 13 per cent. This meant that on average drivers are spending £133 a year more on fuel than they thought they would.
The vehicle that missed by the biggest margin was the Mitsubishi Outlander PHEV hybrid, which is claimed to do 148mpg but only managed 67mpg. The Volvo V60 plug-in hybrid, supposed to do 155.2mpg, came up well short at 80.7mpg. The third worst was the Jeep Grand Cherokee, which officially does 37.7mpg but could only manage 24.4mpg.
Official mpg testing is due to be changed in 2017, but the car industry is petitioning to delay the overhaul until 2020.