Green NCAP has published the results from its latest round of real-world emissions testing, which includes plug-in hybrid (PHEV) models for the first time.

Among the models tested by the independent emissions assessment programme where PHEV variants of the Toyota Prius, Kia Niro and Mitsubishi Outlander.

Green NCAP, which is part of Euro NCAP, said the tests show that not all plug-in hybrids offer the same environmental benefits.

Toyota’s Prius impressed judges the most and was awarded a four-star rating. The Kia Niro followed closely with 3.5 stars, but the Mitsubishi Outlander was given a two-star rating - less than some of the latest Euro 6 compliant petrol or diesel cars.

Euro NCAP Chairman, Niels Jacobsen, said: “The Outlander shows that a big, heavy vehicle with a limited driving range is unlikely to offer any benefit over a conventional car. On the other hand, Toyota, with its long experience of hybrid technology, has done a terrific job and the Prius, properly used, can offer clean, efficient transport.

“It depends on the implementation and hybridisation strategy but what is true of all PHEVs is that they need to be charged regularly and driven as much as possible on battery power if they are to fulfil their potential.”

Green NCAP acquires used examples of each model and conducts tests both in laboratories and on the road to highlight vehicles that go above and beyond the required standards for type-approval.

Only two cars were given a five-star rating in the latest round of tests: the hydrogen-powered Hyundai Nexo (pictured) and the fully-electric VW ID3.

The Mercedes A-Class (A180d) and BMW 1 Series (118i) both received 2.5 stars, while Audi’s A3 (1.5 TSI) was given a three-star rating.