E-Power, the electricity company backed by Esat founder Mr Denis O'Brien, has won a judicial review of a decision by the Commissioner for Electricity Regulation to the limit the power supply it purchases from the ESB to sell on to its customers. This is the first time the regulator, Mr Tom Reeves, has been challenged in the courts.

The company claimed new tariffs for the sale of surplus ESB power - known as "top-up" - and a limitation on its availability "made a mockery" of competition.

"We believe that the Commission is, in essence, stating that we are buying too much and that we need to be limited," said its chairman, Mr Leslie Buckley. "The new charging structure would mean that ePower would be forced to pay between 20 per cent and 260 per cent more for power . . . Therefore we would be paying more than industrial customers are paying today in the retail market to the ESB."

E-Power is linked with Ireland Power, a consortium co-owned by BP Amoco, which plans to build an electricity generation plant at Mulhuddart, Dublin. Because it does not yet generate its own electricity, the company purchases most of the power it sells from ESB surpluses.

But Mr Reeves cited a "letter of clarification" from the Department of Public Enterprise when he proposed the change. It stated that it would be incorrect to interpret a policy direction by the Minister for Public Enterprise Ms O'Rourke as implying that the ESB should be required to provide unlimited power to the independent sector on demand.

Mr Reeves' spokesman declined to comment on the case.