Low carbon cars

Most people are aware by now that hybrids aren't necessarily the most carbon-efficient cars on the market, but just how do you go about choosing a low emission car? The Department for Transport offers some advice on its website, not just about choosing a car but also about how to drive it efficiently. The driving tips are a tad obvious, but good advice nonetheless, and there's more of the same here.

The question of choosing a car is a little more tricky. For a start, only new cars are included in the rankings - indeed, only new cars rated "top 10" by What Car? magazine. Because there's a second hand market for cars, we can console ourselves that the one we discard will be re-used, however there's a good chance that further down the food chain somebody will replace a car that has no market value and will end up as scrap. Keeping our car for longer could therefore be a more sustainable option than trading up to a fuel efficient one, as long as it's not a real gas-guzzler, but I haven't yet managed to find a source of comparisons that includes previous models.

New Vehicle Excise Duty bands to be introduced next April will ensure that the most polluting cars pay more tax. The current 7 tax bands (A to G) will be expanded to 13 (A to M). Owners of cars in Band A do not pay anything. From April 2009, owners of cars in Band M will pay £440, increasing to £455 in 2010 - and there a also new "showroom tax" on new cars which pushes a Band M car's tax up to £950 in the first year.

Only two cars on the What Car? list fall into band A and attract zero tax: the Volkswagen Polo 1.4 Tdi and the Seat Ibiza 1.4 Tdi (which uses the same engine). Both have emissions of 99g CO2/km. But they aren't the cheapest to run: for example the Ford Focus 1.6 Duratorq TDCi has better fuel economy which more than offsets its Band B tax liability, although its emissions are 114g/km. There's a useful article on economical motoring here.