How we did the tests

Using high-tech fuel-flow meters and the latest satellite-navigation timing gear, we measured economy at a steady 30mph, 40mph, 50mph, 60mph all the way up to 100mph.

To make sure our results weren't applicable to just one make and model, we tested five cars from five different manufacturers - a Toyota Aygo, Nissan Qashqai, Volkswagen Passat, Citron C4 Picasso and a Land Rover Freelander.