Around 18,000 buildings, including town halls, museums, schools and job centres, are being tested to discover their energy efficiency on a sliding scale where A is the best and G is the worst.
New buildings fared badly, raising questions about the validity of sustainability claims made by architects and developers. London's City Hall scored E despite opening in 2002 and being described by its architect Foster & Partners as a "virtually non-polluting public building".
The government estimates that almost a fifth of all carbon dioxide emissions in the UK are caused by non-residential buildings.
