1. Honda Insight (00-05)
Parker's says: The pioneering Insight was Honda's first petrol-electric engine 'hybrid' - a car with both a petrol engine and electric motor. It may be quirky to look at, and it only seats two, but there's strong demand among buyers for it and as a result used values remain surprisingly high. Although launched in 2000, it's only those registered from March 2001 that qualify from free Road Tax...
2. Toyota IQ (09 on)*
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Parker's says: Toyota's stylish iQ is a low-cost, high-quality city car with a difference: it's the smallest four seater in the UK. But despite being less than three metres long, it's brimming with space-saving tricks and the cabin is deceptively roomy - particularly for front passengers...
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3. Ford Fiesta Econetic (09 on)
Ford says: The ultimate choice for environmentally aware drivers who don't want to sacrifice driving quality, style or presence. With all the glamour and elegance of the other new Fiesta models, the ECOnetic offers a class-leading, low CO2 emissions performance of 98g/km...
4. SEAT Ibiza Ecomotive (09 on)
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SEAT says: The Ibiza Ecomotive sets a new benchmark for ecologically-friendly cars by reducing the CO2 emissions to a minimum.Thanks to new on board software and a Diesel Particulate Filter (DPF), CO2emissions have been slashed to a meagre 99 g/km...
5. Smart Fortwo Coupe (08 on)
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Parker's says: The latest Fortwo is a little larger, more practical and more comfortable than before with better refinement and an improved gearchange. It is still at home in urban environments where it is very easy to drive, but now it is also easier to live with on the motorway too. Diesel versions are free to tax, others are £35...
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6. Volkswagen Polo Bluemotion (02 on)

Volkswagen says: We care as much as you do about the environment so we design our cars to have minimal impact on it at every stage: during manufacture, while on the road and at the end of their lives. Our Polo BlueMotion for example, is currently one of the most efficient cars of its class...
* Applies only to manual transmission IQs