David Cameron, the Conservative leader, has a wind-turbine on the roof of his Notting Hill home. Gordon Brown, who will shortly face him across the dispatch box, has solar panels atop his dwelling beneath the grey skies of Fife.

This "greener than thou" one-upmanship has become a key component of the political culture. It found its latest expression this week when Mr Brown, prime minister-elect, announced he wanted to create five "eco-towns" featuring 100,000 environmentally friendly homes on brownfield sites.