It's been well known in the car industry that official fuel economy figures should be taken with a pinch of salt.
In the wake of the Volkswagen emissions scandal last year, WhatCar? magazine began work on a more realistic economy test. The process was put together in conjunction with experts to make the results as accurate as possible, and the first results are now coming in.
Shockingly, the cars tested so far typically use about 30 per cent more fuel than official figures say they will. The most efficient car tested was the Vauxhall Astra 1.6 CDTi 110 Ecoflex, which returned 56.3mpg. However, this was a long way off the advertised 83.1mpg.
Other cars to fall well short of their official figures include the Volvo S90 D4, which registered a 37.8 per cent shortfall and the Audi A4 3.0 TDI 218, which was 36.2 per cent worse off.
Earlier this week, vehicle testing company Emissions Analytics released details of its own tests. Incredibly, it said that the only car it had analysed in the last two years that beat manufacturer claims was the Aston Martin Vantage Coupe.
Speaking about the system used in official testing, Nick Molden, chief executive of Emissions Analytics, said: "The current New European Driving Cycle (NEDC) test is done in a laboratory and so it does not have hills to strain the engine, or the harsh braking and acceleration of the real world.
Check out the gallery to see the 10 worst offenders from the figures released by WhatCar? magazine.