After all, what about the higher price of organic food, hybrid cars, energy-efficient appliances, and light bulbs?

The three-bedroom, two-bathroom villa has thermal insulation, solar water heating and energy-efficient appliances.

But the couple decided that it would be just as cost-effective in the long term to install energy-efficient appliances.

The walls of the houses are 6in (15cm) thick and there's state-of-the-art insulation, condensing gas boilers, energy-efficient appliances and water-conserving plumbing systems.

Other measures up for inspection include the predictable double-glazing, roof and wall insulation, underfloor heating, energy-efficient appliances and water-saving lavatory cisterns.