Hybrid cars Hybrid cars use a conventional petrol engine as well as an electric battery that charges as you drive and automatically switches on when the car slows down, making city driving more eco-friendly. These cars cost around two-thirds less to run than a petrol car, have reduced road tax and are exempt from the London congestion charge.

Electric cars With no exhaust emissions, electric cars are currently the most eco-friendly way to drive (assuming your electricity supply comes from a renewable source of course!). Plug them in, charge up for a few pence and away you go. Electric cars are really only suitable for local driving as they have a typical range of about 40-50 miles and a top speed of about 50 mph. However, technology is fast improving.

Liquefied petroleum gas (LPG) Adapting your car to run on LPG typically costs £1000 - £2000, but it is more efficient than petrol and produces less pollutants than diesel. A full tank will cost around half the cost of petrol, although the cost of new LPG cars will be higher - typically £1200 - £2000 more than for non-LPG versions.

Petrol versus diesel? Diesel cars are more fuel-efficient than petrol-driven ones - burning a litre of diesel creates more CO2 than burning a litre of petrol, but the engine efficiency just about makes up for that. However, diesel will create more dirty emissions such as nitrogen oxides and particulates that can affect health. If you are considering buying a diesel car, choose one with a diesel particulate filter (DPF), as this will reduce these emissions. That said, if you live in an urban area and drive a petrol engine that uses the latest low-sulphur fuel, it will be greener than diesel (source: Friends of the Earth).