As such a large cost of motoring, it's little wonder that fuel efficiency is such an important consideration when buying a new car.

But how accurate are most mpg figures? Not very, if last week's Which? survey is anything to go by. Of the 200 cars they tested, just three hit the manufacturer’s fuel efficiency figure – namely the 1.2-litre, five-door, manual Skoda Roomster; the 2-litre version of the Mazda 3 Fastback; and the 2-litre, five-door, automatic diesel model of the Skoda Yeti.

Of the 197 models that were judged to have inaccurate mpg figures, the worst offender was the Mitsubishi Outlander PHEV hybrid, which managed just 67mpg – while its official figure was 148mpg. Quite a discrepancy, if true.

While the cost of fuel has come down recently, it may not stay that way. A car's mpg figure remains a very important piece of information for those looking to purchase a new car.

In a similar vein to the Which? report, What Car? also carried out a range of tests recently, on the most fuel-efficient small cars available. They too found discrepancies in the listed mpg figures.

The Citroen C3 1.4 e-HDi 70 Airdream had an official mpg figure of 83.0, yet the What Car? test suggested it was 70.3mpg. However, it was still judged to be the most fuel efficient small car on the market.

The second most fuel efficient car according to What Car? was the Citroen DS3 1.6 e-HDi 115 Airdream, with an official 74.4mpg figure. Its true figure was 63mpg.

Which? tested the cars at higher speeds, and with air conditioning, headlamps and radio switched on.

The European Commission is set to introduce a new testing procedure in two years' time, but faces pressure from the car manufacturing industry to delay it until 2020 – ostensibly so that the new test is not rushed out "to meet unrealistic deadlines, so that it is robust".

By Craig Hindmarsh