Why are official tests wrong?

* Official fuel economy figures tested * We find wildly differing results * 26 cars tested...

Why are official tests wrong?

A typical small family car can accelerate from 0-62mph in 10 or 11 seconds, if you give the engine and gearbox a real workout. Driven normally, though, it would take between 20 and 25 seconds to reach motorway cruising speeds.

That's a far cry from the official New European Drive Cycle (NEDC) economy test, in which even in the fastest acceleration phase of the extra-urban part, cars have an extraordinarily leisurely 50 seconds to get to 62mph. You'd never drive like this on the road.

The urban test is also extremely gentle. The effort needed is so slight that many petrol-electric hybrids often run on the batteries alone, so they record zero fuel consumption. It is possible to drive on battery power alone in the real world, but you'd have to be incredibly gentle on the throttle, and road and traffic conditions often mean you can't do it for long, especially up a hill.

The NEDC test is also carried out in laboratories at between 20C and 30C. That's probably realistic if you live on the Algarve, but sadly it's just not that warm that often in the UK. Heat and humidity affect how efficiently the engine burns fuel, which impacts fuel economy.