The Toyota Prius: One of the hybrid cars the Hawksworths look at

They are attempting to reduce their carbon footprint, and save money on their energy bills.

We've already worked out exactly how big the Hawksworths' carbon footprint is.

So far we have looked at the pros and cons of travelling by road compared with rail.

We've helped them in their search for a more environmentally friendly fridge.

And we've helped make their home greener with new loft insulation and filling their wall cavities.

Our experts have worked out how much they contribute to global warming and in our latest report, the Hawksworth family test drive some environmentally friendly cars.

Your carbon footprint Calculate your own carbon footprint

In this month's report, Declan takes motoring journalist Quentin Wilson to meet the Hawksworths at the Donington Park racing museum.

They have been looking at greener cars, including hybrid vehicles that use a conventional petrol or diesel engine but also run on battery power generated by the car.

There are many types of environmentally friendly car including electric, hybrids, bio-fuels and of course diesels.

But simply buying a smaller, lighter car which needs less energy to power it can also help the environment.

Buying a green car

You can find out more about buying a green car from Green Car Guide, a specialist website which has some useful advice on how to save money and help the environment.

Please note this is not a BBC website.

Declan looked at five different types of green car in his report (watch again from the link to the right):

The Toyota Prius, was the car driven by Quentin Wilson in our item. It combines a petrol engine with an electric motor which charges its batteries.

It qualifies for lower car tax (unlike a diesel) and is also exempt from the London congestion charge.

The second green car featured was an efficient diesel: the Citroen C4 which can be more economical, and as good as the best hybrid.

Peugeot is planning to launch the first diesel electric hybrid.

The Ford Focus we featured was a bio-fuel five door car. Biofuels are more environmentally friendly than petrol or diesel because they come from renewable sources.

But that in turn can still lead to damage to the environment in processing the fuel.

The fourth example was a G-Wizz electric vehicle which is the most environmentally friendly or carbon neutral green vehicle type.

Of course its usefulness depends on being able to access a re-charging unit which can take between two and a half to eight hours.