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Updated: 29 Jul 2021

Popular full hybrids no 'greener' than top diesel in recent emissions tests

Green testing body's ratings counter assumptions that hybrids always offer environmental improvements over new diesel cars
Skoda Octavia Estate diesel

The Honda Jazz full hybrid has received three and a half stars out of five in environmental testing body Green NCAP's latest independent emissions tests - a result that was matched by the diesel-powered Skoda Octavia Estate.

While three and a half stars is, according to Green NCAP, a good score, the body's 2021 test results show that the environmental benefits of hybrid cars aren't as clear-cut as many assume.

Read on for the full results breakdown and our analysis of why hybrid cars aren't always as green as you might think.

Best cars for 2021 - Which? lab and road tests combine a whole range of factors including emissions, fuel economy, handling and reliability, so you buy a car you can trust.

Green credentials: hybrid vs traditional fuel cars

Hybrids are becoming extremely popular, with a cleaner image that many assume translates to lower emissions and cheaper fuel costs per mile. However, Green NCAP's damning two-star score for the Mitsubishi Outlander plug-in hybrid earlier this year proves this doesn't always match reality.

Diesels, on the other hand, have a (sometimes warranted) bad reputation when it comes to emissions. But the Skoda Octavia Estate, the best-scoring diesel car in Green NCAP's 2021 tests, matches the three and a half stars scored by both the Honda Jazz full hybrid and the Yaris full hybrid from rival Toyota, a brand that is well known for its full-hybrid technology (as with the Toyota Prius pictured above).

Green NCAP says: 'The Skoda Octavia 2.0TDI demonstrates what can be achieved from a modern diesel equipped with the latest exhaust after-treatment technology.'

There are plenty of diesels that have underperformed in Green NCAP's tests, though. For example, in its February 2021 tests, the diesel Land Rover Discovery Sport received Green NCAP's joint-worst ever rating, scoring just one and a half stars (shared in 2021 tests by the petrol Hyundai Tucson). So you definitely need to choose carefully.

This is reflected in our own tests, where we expose that three of the five highest-emission cars are diesels - see our low-emission cars guide for more.

Much like diesel cars in Green NCAP's tests, scores for petrol cars also vary hugely from model to model. Green NCAP has tested 12 fully petrol cars in 2021, with scores ranging from an appalling one and a half stars (the petrol Hyundai Tucson) to three and a half stars (for the petrol Volkswagen Golf).

Do any hybrids beat the Skoda Octavia diesel?

Taking into account all seven hybrid cars that Green NCAP has reviewed so far, only the Toyota Prius plug-in hybrid (results published in February 2021) has narrowly beaten the diesel Octavia Estate's score - by half a star, giving it a four-star rating.

This is despite Green NCAP being generous to plug-in hybrids. The tests assume you start driving with a full battery, and Green NCAP admits many plug-in drivers 'only rarely' drive their cars from this optimal starting point, which could narrow the gap still further.

Best diesel and full hybrid scores

Below, we've highlighted how the best diesels in Green NCAP's 2021 tests (published in February and July) compare with the best full hybrids, and examine whether it's worth opting for a plug-in hybrid instead. You can see the results for Green NCAP's tests of petrol cars in our February 2021 Green NCAP news story.

Good fuel economy and emissions are only part of what makes a car worth buying; click through to our full reviews to make sure the cars are worth buying overall.

Greenest diesels in 2021 tests

Skoda Octavia Estate, £20,827 - three and a half stars

The Skoda Octavia Estate's Green NCAP score, published in February 2021, shows that diesel cars' 'dirty' reputation isn't always justified.

With the exception of electric and other zero-emissions cars, which have all received a five-star green rating so far (see below), it's received the joint-second-highest rating from Green NCAP out of the 28 cars it's reviewed so far in 2021. It's beaten countless petrol models and even some hybrids.

Green NCAP recognises it for 'scoring highly in all three areas of assessment', including for energy efficiency, clean air and greenhouse gas emissions, saying it's a 'remarkable achievement' for a purely combustion engine car. The clean air test measures air pollutants like NOx that are a particular problem in cities.

It's an even more exceptional performance when you consider this is an uncompromisingly large car, promising masses of space for passengers and luggage.

Green NCAP hasn't yet tested its petrol mild hybrid engine option, but we have, so you use our assessments to directly compare whether that provides even better environmental performance over the already stellar diesel.

Discover the exclusive results in our Skoda Octavia Estate review.

Peugeot 208, £16,752 - three stars

It may not have put in quite as strong a performance as the Octavia Estate, but Green NCAP says that the diesel version of the all-new Peugeot 208 (results published this July 2021) also put in a 'very respectable performance' in its tests.

It performs strongly in all Green NCAP's assessment areas, with just one gas (N2O) emission in its warmer test scenario rated as 'poor'.

The 208 certainly has an eye-catching design, and Peugeot promises a higher-standard interior quality compared with previous generations - we've put it through our tests to see if it lives up to expectations.

See whether this could be the ideal small hatchback for you in our Peugeot 208 review.

Seat Leon, £20,405 - three stars

Green NCAP says the new Leon 'greatly impresses' in its tests, published in February 2021. Its three-star score is helped by the latest emission reduction technology, including a three-way catalyst, selective catalytic reduction and a diesel particulate filter - all working to clean the exhaust gases before they enter the atmosphere.

It also praises the car's high energy efficiency, saying this was aided by the 'well-matched' seven-speed automatic gearbox on the model it tested.

The Leon is, in fact, built on the same platform as the Skoda Octavia and latest-generation Volkswagen Golf. Green NCAP hasn't tested the diesel Golf, but it did test the petrol version of the Golf earlier this year. It just pipped the diesel Seat Leon, matching the diesel Skoda Octavia Estate's three and a half stars in its tests.

We haven't reviewed the new Seat Leon hatchback yet, but see what we thought of its larger estate variant in our Seat Leon Estate review.

Greenest full hybrids in 2021 tests

Honda Jazz, £17,607 - three and a half stars

Honda put all its eggs in one basket when it announced the latest Jazz would be moving to hybrid-only, so it is likely to be pleased by its strong performance in Green NCAP's tests, published this July 2021.

Green NCAP said the car 'impresses' and actually performs better in its clean air assessments out on the road than in the lab. It adds that its emissions of greenhouse gases are 'very low'.

The Honda Jazz is famous for making the most of interior space while maintaining conveniently compact outer proportions.

See if this new model outpaces its rivals in our Honda Jazz review.

Toyota Yaris, £18,599 - three and a half stars

Toyota is synonymous with full hybrids - or to use its own lingo, 'self-charging' hybrids - which it made famous with its original Toyota Prius back in 1997. Nowadays, you can buy any of Toyota's cars as a hybrid, and for some models, it's the only option.

Green NCAP says the Yaris delivers 'impressive results', saying on-road emissions of NOx and CO are 'very low' and that particulate matter emissions (carbon) are 'well controlled'. Scores for energy efficiency and greenhouse gas emissions are also strong.

This fourth generation of the Yaris, launched last year, is only available as a petrol-hybrid - unless you get the petrol-only high-performance GR Yaris version.

Is it good enough overall to compete in the fiercely competitive small hatchback market? Check out our verdict in the Toyota Yaris review.

Should I buy a plug-in hybrid instead?

Euro NCAP has tested three plug-in hybrids (PHEVs) so far; while two perform strongly, with three and a half or four stars, you'll need to drive your plug-in efficiently, and remember to charge the battery to achieve the emissions and efficiency that generated these scores. And one of the three PHEVs tested received a below-par two stars.

Toyota Prius Plug-In Hybrid, £24,729 - four stars

The Toyota Prius was originally available only as a full hybrid (Green NCAP hasn't yet reviewed that version), but now you can also buy it as a plug-in hybrid. This offers a larger battery for those who would like a longer electric-only driving range, which you'd expect to further improve fuel economy (our reviews reveal whether this is true in practice).

Judging by Green NCAP's results, published in February 2021, it's certainly a fuel-efficient and low-emission car. Only zero-emission fully electric or hydrogen cars have received higher scores from the testing body.

Toyota claims you can drive up to 30 miles on electric power alone with this large hatchback, which combines a 1.8-litre petrol engine with two electric motors, offering 122hp overall.

Are environmental credentials all this car can shout about, or is it a superb car overall? Find out in our Toyota Prius Plug-In Hybrid review.

Kia Niro Plug-In Hybrid, £27,546 - three and a half stars

Those looking for a car that runs at least in part on electricity are spoilt for choice with the Kia Niro. As well as the plug-in hybrid, it's also available as a full hybrid and in fully electric guise as the Kia e-Niro. We've reviewed all three.

Green NCAP has only reviewed the plug-in hybrid version, and given it the thumbs up. While the Niro plug-in hybrid's green score isn't quite as strong as the plug-in Toyota Prius, the testing body still says the results are 'good' overall.

Find out whether this is a great all-round car in our Kia Niro Plug-In Hybrid review.

Mitsubishi Outlander PHEV, £31,651 - two stars

We exposed the Mitsubishi Outlander's disappointing Green NCAP results back in February. It's woeful two-star result is as bad as some large diesel SUVs, undermining the environmental credentials that have been a big selling point for the car.

It's a very heavy car, and Green NCAP says its 'relatively low range' in electric-only mode is partly to blame for its rating. However, it says that the car 'scores only modestly' in all its testing areas, with its performance 'no better than many non-electrified competitors'.

In official emissions tests, which differ from Green NCAP's tests, it has low CO2 emissions that give it preferentially low car tax (VED) and company car tax rates. However, in two of Green NCAP's more realistic tests it has rated CO2 emissions as 'poor', including for driving on motorways.

Could this be a great car in other respects? We tell you what you need to know in our Mitsubishi Outlander PHEV review.

What about electric cars?

To date, all electric cars tested by Green NCAP have received a perfect score of five stars. This is because Green NCAP's tests currently focus principally on emissions, and electric cars don't make any - because of this, they don't even have exhaust pipes.

For example, in its July 2021 results, Green NCAP rated the Fiat 500 Electric and awarded it the full five stars.

However, that's not the full story. Green NCAP's tests are getting increasingly more sophisticated, but don't yet take into account the efficiency of the car's charger. This didn't stop the body spotting this issue in its tests, though.

Green NCAP notes the standard charger supplied with the Fiat 500 Electric it tested was 'slow and inefficient', warning that 'in the long term, [buyers] will pay more for grid electricity than would be the case with a better unit.'

The only hydrogen car it has tested, the Hyundai Nexo, has also received five stars.

For a holistic assessment of car driving on the environment, you also need to consider the environmental impact of the car's construction, as well as the generation of electricity to run the car.

The source of the electricity you use is a crucial issue to minimise environmental impact with electric cars - and the cost to your wallet. With this in mind, Green NCAP says it will 'soon take into consideration' electricity power generation in its electric car ratings.

Check our guide for more on electric car charging costs and efficiency.

What is Green NCAP?

Green NCAP is a new initiative which launched its testing in 2020, and is funded by Which? and other consumer organisations. It aims to provide independent ratings on the environmental impact of cars, similar to Euro NCAP's long-established safety assessments through crash tests. So far in 2021, it's put 28 cars through its green assessments.

Green NCAP's lab and road assessments aim to be more realistic than official tests, so drivers get a more accurate picture of what they should expect out on the road.

For instance, most Green NCAP's tests use an ambient temperature of about 14u00baC, which is much closer to the UK outdoor average than the 23u00baC (roughly room temperature) used in official tests. Temperature plays a major role in the efficiency of a car.