You want to do your bit to save the planet but you like driving. Lots of us have green consciences but we don't want to give up our cars - or we simply can't.
The truth is, the only purely-green option is to abandon powered personal transportation altogether. The most environmentally friendly way to get around is to walk, cycle, occasionally use public transport for longer journeys, and never, ever, fly. However, such a lifestyle is within reach for very few of us.
There are, thankfully, lots of options to limit the amount of damage you do to Mother Earth. One of them can begin the moment you fire up your vehicle - improving your driving technique. Gentler acceleration, softer braking and generally anticipating road conditions better can make a surprising difference to fuel economy. You might also ensure your car's engine is well tuned, the tyres are correctly inflated and there isn't unnecessary junk in the boot.
You could convert your car to run on Liquefied Petroleum Gas (LPG) as well as its existing petrol system. Given that LPG is roughly half the price of petrol or diesel and yields only slightly worse mpg figures, it is definitely an option worth taking up. LPG burns more cleanly than more conventional fuels and has lower emissions, but very little difference is felt in performance. Some manufacturers such as Vauxhall offer new or used dual fuel models, while the LPG-converted Smart is probably the most remarkable conversion on the market today. There are around 1,000 LPG filling stations in the UK, with a concentration in the bigger cities - and if you find yourself too far away from one you can still run on petrol, remember.
Similar in concept to LPG is Compressed Natural Gas (CNG). Volvo, for example, offer most of their models with a factory-fitted bi-fuel conversion. CNG is even cleaner than LPG, but there are only about 25 filling stations in the UK, usually catering for refuse trucks. Another alternative fuel, biodiesel, is used widely in parts of Europe and has found favour with some local authorities here. Somerset County Council will soon be running wheat-powered Ford Focuses. Some filling stations will sell you a 5 per cent biodiesel blend (see www.biodieselfillingstations.co.uk).
Alternatively, you can go electric. True, the energy still has to be generated somewhere, but power stations are more efficient than the internal combustion engine and pollution is taken away from congested cities. These cars usually have quite a small range, however.
Most practical for now are probably the few hybrid cars on the market. These cleverly combine small conventional petrol engines with an electric motor. The engine charges the batteries when it is on, but it is not needed, for example, when going downhill or during heavy braking - and it automatically switches off at traffic lights. We have the Toyota Prius, the Lexus 400h SUV and the Honda Civic IMA to choose from here, with a new, funkier, version of the Honda promised next year. Hybrids tend to have a high purchase price, so make sure the economics work for you as well as the ethics.
In a decade, though, we'll all be talking about hydrogen fuel cell cars, which emit only water. They will still need energy to produce their source fuel - hydrogen - but many think they are the wave of the future. Honda is pioneering their use in the US, and buses powered by hydrogen fuel cells are running in London, but that's about the nearest most of us will get to that technology for some time.
The most disappointing aspect of trying to drive green is the official attitude. Fine words pour from the mouths of UK ministers and EU officials, but a wrangle between them means the powershift scheme, which offered grants for about £1,000 to £1,500 to people buying or converting to green cars, has been suspended since March. Even without such grants, though, green motoring can make good ethical, environmental and financial sense.
1. LPG Smart
The Smart is quite green anyway, but this conversion is cleaner and cheaper to run. £6,810 + £1,996; MPG 50+; Top speed 84mph; Range between refuelling 250 miles; CO 2/km 90g
2. Toyota Prius (hybrid)
Favourite of Hollywood stars and a thoroughly reliable proposition. £17,545; MPG 65.7; Top speed 102mph; Range 104 miles; CO 2/km 104g
3. G-Wiz (electric)
Two seater billed as "the greenest car available" and carbon neutral. £6,999 (special offer); MPG n/a; Top speed 40mph; Range 40 miles CO 2/km: nil
4. Aixam Mega (electric)
Very odd-looking vans and pick-ups. £9,590 (pick-up version); MPG n/a; Top speed 30mph; Range 62 miles; Co2/km: nil
5. Volvo V70 Bi-fuel (petrol/CNG)
Often sold to local authorities. £25,708; MPG 30.1; Top speed 127mph; Range 400 miles; CO 2/km 169g/km
6. Vauxhall Corsa Dual Fuel 1.2 (petrol/LPG)
Manufacturer's own conversion. £12,015; MPG 38.2; Top speed 109mph; Range 644 miles; CO 2/km: 119g
7. Morris Minor (petrol)
Greener than it looks and ready to go on and on and on. £400 to £5,000+; MPG about 40; Top speed 75mph; Range 260 miles; CO 2/km not measured
8. Lexus RX400h (hybrid)
Proof that 4x4s don't have to be gas guzzlers. Technically similar to Prius. £35,485; MPG: 34.9; Top speed 124mph; Range 490 miles; CO 2/km: 192g
9. Honda Civic IMA (hybrid)
Alternative to Toyota Prius. £15,230; MPG 57.6; Top speed 108mph; Range 640 miles; CO 2/km 116g
10. Citroen C2 1.4 Diesel
Standard but with low emissions. £9,095; MPG 68.9; Top speed 103mph; Range 640 miles; C0 2/km: 107g