When in London, go greentomato cars. They are a private car hire service that uses the Toyota Prius in efforts to be more environmentally friendly. The Prius runs on petrol and an electric motor in tandem. It emits less than helf the amount of CO2 the black cabbies do - bless 'em. In the busy traffic of cities, switching to electric is a great environmental solution and makes less noise too.
Check out grentomatocars.com. They have some energy saving tips there as well that are quite entertaining. Cheers!
