Drivers could be over-spending more than £4bn on fuel

Research by consumer motoring website HonestJohn.co.uk suggests official fuel figures cost UK drivers up to £4.45 billion per year collectively.

The website invited drivers to submit how many miles their cars actually do to the gallon. To date is has collated more than 30,000 entries, covering all major manufacturers and models, with the majority failing to meet official figures.

On average cars only achieve 88% of their official fuel consumption figures, forcing drivers to spend around an extra 2p per litre every time they fill their tanks.

The underlying message from the results seem to suggest that drivers of older cars are able to achieve the official figures more easily, but as the drive to offer competitive CO2 emissions for taxation purposes has taken hold, more recent models seem to have been optimised for the official test cycle and perform less well in real-world driving.

According to the research the worst performing car was the Mercedes-Benz B-Class (2005-2012 generation), which on average achieves just 71.2% of its official fuel economy rating.

The Lexus CT200h and Range Rover Evoque come a close second and third in the worst performing stakes, achieving 73.0% and 73.4% respectively.

The Vauxhall Astra Sports Tourer (2010-) is also one of the UK’s worst performing cars, managing to achieve 74.0% of its recorded fuel economy.

On paper it is capable of up to 70.6mpg, but of those owners who have submitted figures to HonestJohn.co.uk none have reported a figure higher than 55mpg.

The Audi A1 fares little better and is fifth worst, managing on average only 46.8 miles to the gallon, 74.2% of its official consumption figure.

Land Rover may be responsible for one of the worst performing cars, but it is also responsible for the best: the Defender achieves 105.4% of its official test result.

Second place is taken by the Toyota Celica with owners reporting 103.8% of its official consumption.

The Jaguar S-Type also exceeds expectations, achieving an average of 33.3 miles to the gallon, 3.6% better than official figures permit.

The previous Nissan Micra K12 (2003-2010) and the Mercedes-Benz E-Class (2002-2009) finish third and fourth, achieving 102.7% and 102.1% of their official fuel economies, while the Honda Civic Type R (2007-2011) comes a  close fourth with a Real MPG ratio of 102.1%.

While drivers might buy cars informed by official (laboratory tested) fuel consumption figures, the research shows actual rates of fuel consumption can only be measured by assessment of engine performance in on-the-road mile per gallon figures.

Honest John said: "Rather than attack the EC figures, which are now the basis of car and company car taxation, we prefer to offer realistic figures achieved by real motorists to be used alongside official guidelines."