A coalition of leading UK businesses, environmental charities and MPs have today written to environment secretary, Hilary Benn, and business and enterprise secretary, John Hutton, calling for standardised rules for corporate on carbon emissions.

The coalition, known as The Aldersgate Group and including BT and United Utilities, argues that the value to companies in disclosing their carbon footprint is being undermined by the lack of a recognised standard for measuring emissions, and urges the government to introduce a "common protocol" for all firms to follow.

"Current reporting levels are still too low, and what is disclosed is not comparable because of the use of different calculation methods," says the letter. "The lack of transparency… undermines the comparative advantage that should accrue to companies with good carbon reporting and control."

Previous attempts to encourage companies to report on their environmental impacts were killed by the government last year when the then-Chancellor Gordon Brown scrapped plans for Operating and Financial Review legislation that would have forced them to report annually on non-financial impacts to their business.

The release of the letter was timed to coincide with today's UK launch of research from the US-based Carbon Disclosure Project showing that many firms are still failing to publish data on their carbon emissions.

The report, which was released in the US last month, found that while 95 per cent of FT500 companies had implemented emissions reductions programmes, less than half of FTSE350 were publishing carbon emissions data.

Speaking at the launch event earlier today, climate change minister Joan Ruddock said investors had a responsibility to increase pressure on firms to report on their environmental impacts.

"Investors have a particularly key role to play in this," she said. "They should give consideration to environmental and social credentials, sending out signals to the financial markets to say that carbon disclosure is vital and show companies that it will affect their investment decisions."