Justin Rowlatt installed a wind turbine to save energy

This means that it would take 150 years for turbines- costing �1,500 - to save enough money to pay for themselves.

With UK wind speeds of 5.6m/s (18.3ft/s), many Britons would not benefit from high savings.

Chief of Windsave, David Gordon, told Panorama: "[Between] 4-6 metres, you'd save about �10 a year.

"Six metres onwards and you could save up to �50 to �100."

'Carbon challenge'

In Panorama's Go Green Or Else report, BBC journalist Justin Rowlatt spent a year trying to reduce his carbon footprint.

As part of a "carbon challenge" set by Professor Tim Jackson of Surrey University, to reduce his family's impact on the environment, Rowlatt decided to try to install a wind turbine as a way of generating carbon-free electricity.

Windsave offered him one, but seven months later - and three days before it was due to be installed - the company withdrew its offer saying his house was not suitable.

After the offer was withdrawn, David Gordon explained there was not enough wind at Rowlatt's London home.