The ESB, Synergen and Edenderry Power were forced to purchase over 1.5 million tonnes of carbon credits from other more environmentally friendly companies to cover their excess emissions.

Sources within the energy industry said that there was increasing concern that state companies are less aggressive at meeting their targets than privatelyowned firms, due to deep-rooted vested interests.

They also said that the ESB's continued use, due to political interference, of older, less efficient plants meant that private firms such as Viridian, which operates Huntstown power station, are also unable to meet their targets as they have to "step in" when the ESB's plants break down.

"There doesn't seem to be any incentive for them to clean up their plants or to try and increase the efficiency of their plants, " said a spokesman for Viridian. Of the three companies, the ESB exceeded its target by the greatest amount, emitting over 1.1 million tonnes of carbon dioxide above its allowance.

This would have been higher but for a flaw in the trading scheme which meant it received full credits for a power station it closed during the year and several stations that were out of service for prolonged periods.

Synergen, which is 70% owned by the ESB, missed its target by over 201,000 tonnes even though it runs a single power station.

The final firm, Edenderry Power, exceeded its allowance by almost 233,000 tonnes. The company, which runs a peat-fired power station in Co Offaly, was privately-run during 2005 but was bought by Bord na MA3na last October.

A spokesman for the ESB said that it had missed its targets in 2005 because "the EPA placed a greater onus on the electricity sector as a whole in line with a government policy direction and demand for electricity continued to grow strongly".

He said that the company had taken a number of steps to reduce its emissions, including the replacement of older plants and the use of biomass fuel in its peat-fired stations. Dermott Kelly, Bord na MA3na's director of energy, said that Edenderry Power had been trying to use biomass fuel to cut emissions since 2002 but had been prevented by local protestors, who were concerned about proposals to burn meat and bonemeal there.

Meanwhile, a spokesman for Quinn Cement, the one non-energy firm among the five firms that missed their targets by the greatest margin, said the EPA had not granted it enough credits.

"The EPA for some reason uses figures from 2002 and 2003 as the base year for credits, when our plant was in its infancy. That's why Quinn Cement currently exceeds it."

He said the firm was in discussions with the EPA about increasing its allocation.