1. Peugeot iOn - 88g/kmAs a fully electric car, nothing actually comes out of this vehicle while it is being driven, but CO2 is released through the production of the electricity used to charge it. We used the latest figures from the Department for Energy and Climate Change, which state that an average of 521 grams of CO2 are emitted per kilowatt hour of electricity, to calculate the iOn's CO2 emissions.
2. Volkswagen Polo - 99g/kmAll the VW Polos we've tested have low emissions, but it's the 1.2 TDI BlueMotion diesel that emits the least at 99g/km. This is exceptionally good and contributes to low running costs. In contrast, the 1.4-litre petrol engine is the worst Polo we've tested for emissions, recording 140g/km.
3. Vauxhall Ampera - 102g/kmThe Ampera is a 'range-extender' hybrid. This means is can run on electricity with no range anxiety, as it also has a petrol engine. Short distances can be completed in electric mode only, so there are zero emissions. However, according to our tests of the car in combined electric/petrol mode, it actually emits 102g/km of CO2.
4. Smart ForTwo - 105g/kmThe Smart ForTwo is one of the world's most recognisable city cars. It's only got two seats, but is surprisingly spacious for its driver and passenger. The 0.8 CDI engine promises low carbon dioxide emissions levels, and it recorded 105g/km in our tests. However, the official manufacturer CO2 claim is 88g/km, so this car still benefits from free road tax.
5. Nissan Leaf - 106g/kmOne of the first battery-driven, family-sized cars available in the UK, the Leaf offers low running costs. Using the same system as the
Peugeot iOn, we measured the emissions at 106g/km. However, the precise CO2 output of the car will vary depending on exactly how it is charged. For example, if charging is supplemented by solar power, then that figure will be lower.
6. Volkswagen Golf - 108g/kmThe
VW Golf has a wide range of emissions depending on which engine you opt for. The 1.4 TFSI recorded a lofty 160g/km. However, the 1.6TDI BlueMotion impressed our experts with only 108g/km CO2 emissions, which ensures car tax is kept to a minimum.
7. Toyota Auris - 109g/kmToyota launched this hybrid version of its Auris back in 2010. The Auris hybrid is smooth and quiet, and has so far proved very reliable. As for emissions, there is still some work to be done to hit the 2020 target, but at 109g/km it is one of the best performers at present.
8. Honda Insight - 111g/kmRivaling the Toyota Prius in the large cars class, the Insight hybrid has an efficient 1.3-litre engine. CO2 emission claims of the latest Insight are between 96g/km and 99g/km (bettering the original version's 101g/km), however our tests recorded 111g/km.
=10. Audi A1 - 111g/kmTaking manufacturer claims, no Audi A1 has official C02 emissions of more than 125g/km, meaning you'll pay no more than £95 a year in tax. The most efficient engine we've tested is the 1.6 TDI - measuring 111g/km, 8g.km higher than the claim.
=10. Toyota Prius Plug-In - 111g/kmThe brand new Prius Plug-In builds on the original Prius's eco-friendly reputation. The hybrid petrol-electric 1.8-litre engine offers electric-only driving at speeds up to 62mph. But, once the petrol kicks in, emissions increase to a recorded 111g/km.