Bord Gáis has entered the residential electricity market, with a guarantee to customers that its prices will be at least 10% lower than the ESB.

The company's chief executive, John Mullins, said it would be a simple process for ESB customers to switch to Bord Gáis. The offer is open to all 1.8 million registered households who use electricity.

This announcement by Bord Gáis amounts to a huge shake-up of the residential electricity market and, the company claims, will result in immediate and substantial savings for customers.

From today, any ESB customer will be able to switch over and get their electrify from Bord Gáis by either phoning the company or going online.

It hopes to expand its customer base to more than a million people in three years, by promising its bills will always be at least 10% lower that the ESB in the first year with a guarantee of lower rates against any further changes in ESB prices.

Additional discounts are available to customers choosing to pay by direct debit and to existing Bord Gáis natural gas customers.

Mr Mullins said the double digit guarantee would remain in place, no matter what cuts the ESB introduced; adding that there would be no penalty if a customer wanted to switch back to the ESB.

'We are confident that customers will make the switch to electricity from Bord Gáis Energy,' Mr Mullins said. 'We look forward to real competition in the Irish energy market, which has clear benefits to customers and Ireland Inc,' he added.

On gas prices, Mr Mullins said he believed that they would go down considerably this year - with prices more than 25% lower next December than they are today.

Meanwhile, the ESB said the residential market has been open to competition since February 2005 and it was open to all competitors to charge what they like.

In a statement this morning, it said it welcomed any new competition into the market. But the ESB said it was required to charge the rate set by the Commission for Energy Regulation and was not allowed to discount from that rate.