Eircom has said it regretted overcharging some of its customers over 12 years yesterday, but added that it could not guarantee that its billing system would ever be 100 per cent accurate.

Mr David McRedmond, Eircom's commercial director, told the Joint Oireachtas Committee on Communications that billing systems were becoming experientially more complex nowadays.

"We are not guaranteeing that there will be no errors in bills, as there are errors in every billing system," said Mr McRedmond, who added that he regretted the the overcharging error occurred.

The committee is investigating Eircom's admission in the summer that it overcharged 31,500 customers by €409,000. The firm said the overcharging was a result of a system error.

Mr McRedmond said when the firm found out that some customers were being charged twice for some services, it reviewed the situation over the past 12 years.

He also said he agreed with comments made recently by Eircom chairman Sir Anthony O'Reilly that the telecoms firm was excessively criticised in the Republic.

Several firms including Vodafone, NTL, O2 and Esat BT have also been involved in overcharging incidents this year.

Mr John Doherty, chairman of ComReg, told the committee the regulator needed more enforcement powers to act as a deterrent to companies in the sector.

Mr Doherty said some firms could have handled the recent overcharging issues better.