The UK's biggest CO2 offenders unveiled

In Salford, the Imperial War Museum North, designed by Daniel Libeskind and opened in 2002, scored a G, the same as its 91-year-old sister museum in London.

The government estimates that almost a fifth of all carbon dioxide emissions in the UK are caused by non-residential buildings, and environmental campaigners said the findings mean the government must launch an urgent refurbishment programme to slash carbon emissions.

The Natural History Museum spends £1.4m a year on electricity and gas - a figure that is expected to double from this month as a result of rising world energy prices. One of the most energy hungry buildings in the country was the National Media Museum in Bradford, a 1960s structure, which scored a G. One in four of the 3,200 buildings assessed so far scored F or G, and the average was D. Only 22 buildings - under 1% - scored A.

"These results show our leaky and draughty public buildings should be a priority target for refurbishment," said Paul King, chief executive of the UK Green Buildings Council. "In a turbulent financial climate, lower energy bills will benefit the taxpayer for years to come. If we are to cut our carbon, save money and achieve energy security, our buildings have to be on the front line of this battle."

"We review 350 significant new build projects a year at design stage and we hear a lot of greenwash," said Matt Bell, director of public affairs at the Commission for Architecture and the Built Environment, the government's architecture watchdog. "The knowledge that from now on this performance will be objectively measured should mark the end of that."