According to research by the Institute of Advanced Motorists common driving errors - such as an aggressive driving style - can increase fuel consumption by 45%, more than offsetting the benefit of a fuel-efficient car.

Typical 'errors' (and their cost in fuel consumption) include:

  • Under inflated tyres (3%)
  • Roof storage (20%)
  • Air conditioning (10%)
  • Aggressive driving (15%)
  • Speeding (15%)
  • Short journeys (100%)

Overall, says the IAM, this would give a supposedly fuel-efficient car like Ford's Focus Econetic the same fuel consumption as a seven-seat Ford Galaxy.

They're interesting figures, but we're not told how the IAM arrived at them.

Four years ago I did my own set of fuel consumption tests, the results of which were reported in a feature for Carbuyer magazine. Driving with economy in mind our test car, an Audi A3 2.0FSI, delivered an excellent 62mpg on a mixture of roads intended to replicate the official Extra-Urban conditions. Aggressive driving increased the fuel consumption of our test car to around 24mpg.

That's an increase not of 15%, as the IAM suggests, but more than 150%!

Still, aside from some concern about the veracity of the numbers it's difficult not to side with the IAM and its message. Says IAM Head of Technical Policy and Advice, Tim Shallcross: "If the government is serious about getting motorists to reduce CO2 emissions, the IAM says more investment in driver education and information is needed, rather than extra taxes that motorists suspect are more about revenue-raising than improving the environment."