True MPG: which cars beat their official figures – and which are farthest away?

Our True MPG tests show what fuel economy you can really expect from a car, with some models beating their official figures but others falling more than 26% short...

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New petrol, diesel and hybrid cars are on average 6.3% less efficient in real-world conditions than the official WLTP figures suggest, What Car? has found.

We put 96 popular models through our independent True MPG test, with the worst performers 26% down on their official figures, and the best almost 19% up.

WLTP is, however, a lot more accurate than the old NEDC system, which it replaced in September 2018; a previous sample of 159 vehicles type approved to NEDC standards showed an average discrepancy of 20.2% between True MPG and the official results, with the worst performers as much as 40% less efficient than advertised.

To ensure accuracy and repeatability, our True MPG tests are conducted in strictly controlled laboratory conditions, but they are based on a real route that takes in town, rural and motorway driving.

As a result, they reflect what's achievable if you’re driving gently and sticking to speed limits but aren’t resorting to any unrealistically slow acceleration or special 'hypermiling' techniques.

Which of the latest models were farthest away from their official figures, though, and which over-achieved? Let's take a look, starting with the 10 biggest under-performers...