Downing St, the home of Gordon Brown, has achieved only an energy efficiency rating of D with annual C02 emissions of 675 tonnes of carbon. No 10 Downing Street is better than average for its building type. But the prime minister's heating, lighting and air conditioning still create a bigger carbon footprint than a street of 28 families of four living in semi-detached homes, each driving 10,000 miles a year and flying to Spain on an annual holiday.