Eircom has admitted that it supplied incorrect data to the telcoms regulator ComReg relating to the level of faults suffered by its business customers.

The data that Eircom published earlier this week showed the number of faults on business phone lines had doubled but now the telco says the proportion actually dropped slightly.

A spokesman for ComReg said the regulator is "extremely unhappy to learn that we were not supplied the correct figures". ComReg is expected to await a full explanation before it decides what action to take.

Eircom is obliged to publish certain data relating to the performance of its network because as the former incumbent it has a universal service obligation (USO). On Tuesday it published data covering the first two quarters of 2007. This showed that there were 3.1 faults per 100 lines in the first quarter and 6.2 in the second. Yesterday Eircom said the correct figure for the second quarter is actually 2.8.

"There was a mistake in compiling the data," said an Eircom spokesman. "We are delighted that the correct figures show no increase in the level of faults in our network."

Alto, the representative body for alternative operators including BT Ireland, Cable & Wireless, NTL, Magnet Networks and Smart Telecom criticised Eircom for the error.

"I cannot understand how they published figures on their website that show such a disimprovement without checking them properly," said Liam O'Halloran, chairman of Alto. "Personally I think something very strange is going on."

Mr O'Halloran also said the data only relates to Eircom's own customers and not those served by other operators using Eircom lines.

"We are particularly concerned about wholesale customers given the finding last year, on foot of a complaint, that wholesale customers were discriminated against in favour of Eircom's own retail customers," Mr O'Halloran said.

The Eircom spokesman said the company provides data directly to each individual operator but does not publish it.

Mr O'Halloran was also critical of Eircom for publishing six months after the period in question. "Sixty days to gather the necessary material would be more realistic," said Mr O'Halloran.

The deterioration in relations with ComReg comes at a bad time for Eircom as ComReg is drawing up new binding USO targets for repairs and faults which Eircom will have to meet.