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25 Feb 2021

Plug-in hybrid car scores no better than new diesel SUVs in latest emissions tests

Green testing organisation's results show that not all plug-in hybrids have a clear environmental benefit over new petrol and diesel cars

Oliver TrebilcockSenior researcher & writer

The popular Mitsubishi Outlander plug-in hybrid SUV received only two stars out of five in environmental testing organisation Green NCAP's independent emission tests. This is the first time it has rated plug-in hybrid vehicles and the results reveal that buying a plug-in hybrid is no guarantee of getting a cleaner car than some modern petrol or diesel cars.

The Mitsubishi Outlander PHEV has been quite the sales phenomenon for the brand, largely due to its low CO2 emissions in official tests, which differ from Green NCAP's tests, giving it preferentially low car tax (VED) and company car tax rates.

However, Green NCAP's results lay bare how, based on its tests, the Outlander isn't one of the most environmentally-friendly cars on the market.

Also, Green NCAP says the real-world performance of plug-in hybrids is likely to be worse than its test results indicate. This is because the organisation's tests assume you're always starting your journey with a full battery and ending with an empty one, but Green NCAP says drivers 'only rarely' drive their plug-in hybrids optimally and that 'many PHEVs are mostly driven using the combustion engine only.'

If you're only driving your plug-in hybrid on combustion power and and also lugging round a heavy flat battery, it's likely to mean fuel economy is worse than the best new petrol and diesel cars.

We highlight the best and worst performers from each class in Green NCAP's latest tests, including new petrol, diesel, hybrid, hydrogen and electric cars rated, below.

Best cars for 2021 - our car recommendations involve countless Which? lab and road tests for fuel efficiency, emissions, handling and more, plus in-depth reliability data based on real cars. So you can be confident we'll help you buy a car that won't let you down.

What is Green NCAP?

Green NCAP is a new initiative funded by organisations including Which?. Similarly to Euro NCAP, which provides safety assessments on cars through crash tests, Green NCAP aims to provide independent ratings on the environmental impact of cars.

Green NCAP's tests combine lab tests and road tests. The lab tests use more realistic conditions than official tests. For example, the tests use an ambient temperature of about 14°C, which is much closer to the European average than the 23°C used in official tests.

An on-road driving test is also used, which Green NCAP says goes beyond official test requirements to get an accurate assessment of real-world emissions.

Best and worst performers

We reveal the best and worst performers in Green NCAP's latest tests below, as well as the ratings for all the 25 cars in this month's results.

Emissions are only one consideration when buying a car, so be sure to click through the links to our full expert reviews to find out whether a model is right for you.

Best plug-in hybrid: Toyota Prius Plug-In Hybrid (£24,729) - 4 stars

Toyota is well-known for being a leader in 'self-charging' full hybrid technology, where you don't need to plug in your car to charge it However, this plug-in hybrid version of its famous full hybrid Toyota Prius proves it's no slouch with this tech, too.

The Prius plug-in hybrid combines an electric motor and petrol engine. Toyota claims you get zero tailpipe emissions over distances of 30 miles on battery power alone, before the petrol engine kicks in.

Green NCAP's tests cover three areas:

Clean Air assessments check for nasty gases like NOx that cause air pollution in cities
Energy Efficiency checks how much energy is wasted driving the engine
Greenhouse Gas test rates how many gases that contribute to climate change, like carbon dioxide' are released.

The Prius gets high marks in all these areas. Its lowest was six out of 10 in the Clean Air test, but Toyota has since added a gasoline particulate filter to current production models of this car, which should improve its performance still further.

Find out if this is a great car across the board - or has something to hide - in our full Toyota Prius Plug-In Hybrid review.

Worst plug-in hybrid: Mitsubishi Outlander PHEV (£34,934) - 2 stars

Green NCAP tested the newer 2.4-litre petrol engine version of the Mitsubishi Outlander PHEV. It scored below average across the board in these tests, which differ from the official tests.

The Green NCAP tests even indicate it has 'weak' carbon dioxide gas emissions in the organisation's cold and warm-start tests.

This is despite the Outlander officially having low CO2 emissions (as little as 40g/km) - the reason it enjoys favourable car tax (VED) and company car tax rates.

Plug-in hybrid technology is currently much-favoured by car manufacturers seeking to reduce their carbon footprint to meet new emissions legislation.

However, all PHEVs need to be charged regularly and driven as much as possible on battery power for the greatest environmental benefit. And in the case of the Outlander PHEV, based on Green NCAP tests, the best you can hope for even if you do this is a similar performance to some of the latest petrol and diesel cars.

Find the best PHEV for your budget - see all of our plug-in hybrid car reviews.

Best SUV: Ford Kuga (£26,765) - 2.5 stars

The Ford Kuga SUV can be bought as a diesel mild hybrid, and Green NCAP tested the 2.0 EcoBlue Hybrid version. Mild hybrids have small electric motors and can't be driven on electric power alone, but the Kuga proves the technology's potential when it comes to emissions, topping the SUV category in this latest release of results.

Nevertheless, being a SUV, it unsurprisingly still gets a middling score. The Green NCAP tests show its emissions of N2O, also known as laughing gas, are high. This is a potent greenhouse gas which is not currently regulated by official emissions legislation.

We haven't reviewed the new Ford Kuga yet, but see whether its predecessor was anything to shout about in our Ford Kuga (2012-2020) review.

Worst SUV: Land Rover Discovery Sport (£30,358) - 1.5 stars

The Land Rover Discovery Sport and Hyundai Tucson are joint-last in Green NCAP's SUV rankings this month, both getting a woeful 1.5 stars out of five. We've featured the Discovery here as it almost gets zero in the Greenhouse Gas emissions test.

Green NCAP tested the diesel D180-engined Discovery Sport. It performed reasonably in air pollution tests, but poorly for both energy efficiency (due to the car's hefty near two-tonne weight) and greenhouse gas emissions. Both carbon dioxide and N2O emissions were high in most tests.

What's this car like to drive if you need an off-roader? Check out the verdict of our experts in our definitive Land Rover Discovery Sport review.

Best medium car: Volkswagen Golf (£20,730) - 3.5 stars

The Volkswagen Golf, with the petrol 1.5 TSI engine, scored an impressive 3.5 stars out of five. This is the joint best result achieved so far by non-electrified cars in Green NCAP's tests, alongside the diesel engine test of the Skoda Octavia.

The Golf achieved more than six out of ten in both air pollution and energy efficiency assessments, and its 5.3 rating for greenhouse gas emissions is still considered good.

Is this the ideal family hatchback, or is it outclassed in other areas? We give all the answers in our exclusive Volkswagen Golf review.

Worst medium car: Honda Civic (£20,141) - 2.5 stars

Three cars got this month's worst score of 2.5 stars out of five in the medium car class, but the Honda Civic got the lowest scores in the most areas.

Testing its petrol 1.0 Turbo engine, Green NCAP gave it below-par scores for both air pollution and greenhouse gas emissions. High carbon monoxide and ammonia emissions in the more challenging tests were to blame for its air pollution score, and its carbon dioxide emissions were rated as 'weak'.

It's not done too badly overall though - find out if this car excels in other areas in our Honda Civic review.

Best small family car: Toyota Yaris (£19,262) - 3.5 stars

Toyota is a pioneer in 'self-driving' full hybrids, and Green NCAP's tests on the petrol 1.5 hybrid version of the Yaris put the proof in the pudding.

It scored well in all areas, with the results showing you should get great fuel economy with this car.

Is the Yaris just as good across the board? We put it through its paces in our first drive Toyota Yaris review.

Worst small family car: Mini hatch (£15,670) - 2.5 stars

The Mini hatchback was one of four cars to get the lowest rating of 2.5 stars out of five in the small family car class this month, with the Mini generally getting lower scores overall than the other three in Green NCAP's test areas.

It's not too surprising, though, considering its one of the older cars on test, originally launching in 2014. Green NCAP tested the petrol Cooper Steptronic specification.

It doesn't rate really badly though, scoring around four out of ten in each area - a reasonable result for a petrol car.

Could other factors make this the perfect car choice? We reveal all in our Mini hatch review.

All the latest results

Find the latest results for all the 25 cars tested by Green NCAP below. In each case, we've given the typical engine specification that was tested.

Innovative cars

These are cars with innovative driving technology aimed at improving emissions - use the links to read more about how these cars performed in our own tough lab and road tests:

Hyundai Nexo - 5 stars (hydrogen-powered car)
Volkswagen ID.3 (58 kWh) - 5 stars (all-electric car)
Mazda CX-30 (petrol; SkyActiv X) - 2.5 stars (Mazda's SkyActiv technology aims to improve petrol engine efficiency by reducing the need for spark plugs)