Our tests involve driving around corners which, on most cars, draws power from the engine to operate the steering pump and so uses fuel. This doesn't happen in the official test, where the car sits on a rolling road (a stationary test bed that monitors all the car's outputs). Our cars also have to climb some hills.
We run four tests in total, rather than two as in the NEDC, and our urban route alone is longer than the entire official test.
In our urban tests, the average speed is 17mph, there are 12 stops instead of four, and three slow-speed corners taken at 10mph. The car is at a standstill for a quarter of the time during this test, so hybrids and cars with engine stop-start systems still get to strut their stuff.
The same goes for the suburban route, where we include four 30-second pauses to simulate traffic lights. Cruising speeds reach 45mph.
We accelerate harder and cruise for longer in our motorway section, while the 'gentle' test shows what you might expect to get from your car by driving normally and not like an eco-motorist.
Finally, all of our tests are conducted between four and 16C. Apart from a few days of summer, we think that this is far more realistic than the balmy environment of the official test.
Our economy expert
Peter worked for 35 years with the AA, where he wrote exhaustive fuel economy test reports for the company's magazine for members.
The aim of these reports was to include as many objective measurements as possible, including the more meaningful 30-70mph acceleration times that we use and real-world fuel consumption data.
His finely honed tests demonstrated the wide range of fuel consumption that cars could return and, following decades of trails, have proved to be repeatable to within 1.5%.
Since retiring from the AA in 2003, Peter has continued to evaluate cars, engines, transmissions, fuels, oils and components on a consultative basis.