A spokesman for the organisation said one possible contributing factor was that Irish businesses did not become more technically energy efficient during 2005.

He said, though, that it remained unclear what had caused the 2.7% dip in efficiency, which is measured using a complex mathematical model which includes energy usage data from 12 industry sectors but strips out social and economic factors such as climate change.

David Manning, energy executive with employers' organisation IBEC said that he was concerned by the figures and said that they indicated that the government needed to introduce energy-efficiency incentives for businesses.

"I'd be concerned that so much investment has gone into energy efficiency that we've reached a certain point where the economy needs assistance to get where it is going, " he said.

Manning said that the government should introduce schemes such as interest-free loans for energy efficiency work, which are offered by the Carbon Trust in Britain, to ensure that Irish business became more efficient again.

He said that the government could fund the incentives by using the additional money it had raised as a result of rising fuel prices in recent years.

"A lot of extra money has come to the government in the past three years in excise and VAT on fuel sales and, given that we all agree from a competitive and environmental perspective that energy efficiency is the way to go, they should ring-fence this money, " he said.