Britain's climate change emissions may be 12% higher than officially stated, according to a National Audit Office investigation which has strongly criticised the government for using two different carbon accounting systems. There is "insufficient consistency and coordination" in the government's approach, the NAO said.

Using one system, which the government presents to the UN and in public, Britain emitted 656m tonnes of CO2 in 2005, and claims an improvement on 1990 figures. However, the lesser-known but more accurate data in the government's national environmental accounts show emissions to be in the region of 733m tonnes in 2005, a NAO report says today.

"There are two different bases on which the government reports emissions: that required for the UN, and the environmental accounts prepared for the Office of National Statistics ... [which are] more comprehensive as they include aviation and shipping emissions. They present UK progress in reducing emissions in a markedly different light", says the report.