That's despite the introduction of a new, more "real-world" test in 2017.

Research suggests new cars are still around five percent less economical than official figures suggest, despite the introduction of a new, more “real-world” test in 2017. However, the study by consumer magazine What Car? found the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP) system to be much more representative of real economy figures than its predecessor.