Green NCAP on Thursday announced its environmental performance ratings of 25 new cars including, for the first time, plug-in hybrid electric vehicles (PHEVs).

The results for three – Kia Niro, Mitsubishi Outlander and Toyota Prius – showed that not all plug-in hybrids offer the same environmental benefits.

The hydrogen fuel-cell Hyundai Nexo did, however, demonstrate the promise of this developing technology, the organisation said in a statement.

The list of tested cars also included the VW ID.3 BEV launched in Europe and UK late in 2020 and 19 combustion engine cars, of which two – the Skoda Octavia Combi 2.0 TDI and VW Golf 1.5 TSI – stood out from the rest.

"When it comes to environmental cleanliness, pure electric vehicles outshine the competition and, with rising consumer interest, more and more traditional carmakers are getting serious about electric vehicles," Green NCAP said, adding: "Volkswagen's first standalone electric car, the ID.3, reinforces this message, joining the BEVs previously tested with a maximum five-star rating.

"The Nexo also achieved five stars as it proved to be just as clean as a battery electric vehicle and very nearly as energy efficient.

"The result clearly shows the huge potential of the technology  but fuel cell cars are an obvious choice to most consumers only if sufficient hydrogen fuelling stations were available."

Green NCAP said PHEV technology is currently much favoured by manufacturers seeking to reduce their carbon footprint and comply with new emissions legislation. Marketed as offering 'the best of both worlds', battery-powered cleanliness when needed with the driving range of a combustion-engined car, the tests revealed that, even when optimally charged, not all PHEVs are the same.

The Prius impressed most with a four-star rating that beat all but pure electric and hydrogen fuel cell cars. The Niro followed closely with 3½ stars but the [ageing] Mitsubishi Outlander only achieved two stars, less than some of the latest Euro 6 compliant petrol or diesel cars.

The model is being replaced in other markets with, first, a facelift and, starting next April, a full redesign based on a Nissan platform but Mitsubishi said recently it would withdraw eventually from Europe and not introduce any more new models.

Euro NCAP chairman, Niels Jacobsen, said: "People want independent, transparent information about the environmental impact of cars. These PHEV results show why that is so important. Consumers could be forgiven for thinking that, by buying a car labelled PHEV and keeping it charged all the time, they will be doing their bit for the environment, but these results show that this is not necessarily the case.

"The Outlander shows 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 said the Yaris Hybrid further underlined Toyota expertise in electrification with a respectable 3½ star rating but was matched by two ICE cars, the diesel Skoda Octavia Combi 2.0 TDI and the petrol VW Golf 1.5 TSI. These scored the best results so far achieved by non-electrified cars.

Added Jacobsen: "Euro 6 legislation has made a real difference. For the first time, we're seeing cars perform in real world driving the way they promise on the test bench and we should congratulate car manufacturers and emissions engineers for the huge strides they have made in the last few years.

"The future looks like it belongs to electric cars of one sort or another but, for now, consumers face a bewildering choice."