The ESB remains too dominant in the electricity market and its growth should be halted, the private operator Viridian has suggested.

The comments by Viridian chief executive, Mr Patrick Haren, come on the day the electricity market opens further, with 12,000 companies now entitled to pick their own supplier.

About 56 per cent of the market is now open to competition, with the remainder opening up in 2005. Previously, just 1,600 of the State's largest energy-users were eligible to shop around for an electricity supplier.

Mr Haren, a former ESB executive, said Viridian's Huntstown power station was now supplying 10 per cent of Ireland's total electricity requirement but more needed to be done to stimulate competition.

He said customers deserved greater choice and real value for money. "Suppliers want protection against ESB's market dominance in Ireland through its unassailable position in generation. There is no prospect of meaningful competition without further independent generation plant in the market," he said.

The Minister for Communications, Mr Ahern, in a statement, said the further liberalisation should act as an incentive to new market entrants and allow existing suppliers to grow their market share.

Mr Ahern said the liberalisation of the market arose from an EU directive: "Ireland is well-advanced in market opening with our full liberalisation date of February, 2005, being an advance of over two years on the timetable set down by the EU."

He said, in effect, many small and medium-sized businesses would be eligible from today to contract for their electricity supplies from licensed electricity suppliers other than the ESB.

"This latest opening represents nearly a sevenfold increase in the target customer-base for independent players in the market," he said.

But Mr Haren struck a different note. "Our big concern is the total lack of independent power generation to supply the competitive market in which we have to survive. The recent capacity competition was based on long-term ESB contracts and new entrants see only a future of continued ESB dominance in generation. This position is further reinforced by its continued ownership of ESB National Grid," he said.

Responding to recent comments by the Commission for Energy Regulation (CER) that it had no power to break up the ESB, Mr Haren said: "If CER don't have what they need to directly address ESB's dominance in generation, we would gladly join with them in lobbying the Minister to give them the required powers."