More problems have been revealed at Severn Trent

The company said it misreported statistics about the way it handles complaints from customers and enquiries about bills.

The admission echoes a similar problem revealed last month at Southern Water, which will lead to a fine for Southern.

Severn Trent has already been punished for reporting false data to Ofwat about its income and bad debts.

The latest problems, over customer service data, were first discovered in February.

"We have been reporting more favourable data than we should have" said a company spokesman.

Severn Trent said it did not know how much money was at stake but admitted the problems seemed to stretch back several years.

"We are determined to resolve any issues uncovered as soon as possible," said chief executive Colin Matthews.

"We shall continue to work in full and open co-operation with Ofwat and obviously if customers have been disadvantaged then we shall reimburse them."

A final report will be ready in June when Ofwat will launch its own investigation using independent accountants.

Previous problems

In March, Severn Trent agreed to refund �42m to customers because wrong information about its bad debts and income had led the regulator to agree unnecessarily high prices for the company's customers up to 2009-10.

The company is still being investigated by the Serious Fraud Office for also allegedly falsifying its water leakage figures.

These problems first came to light in 2004 after complaints by a whistleblower at the company.

Since then a new management team at Severn Trent has been trying to get to the bottom of the matter.

Consumer watchdog organisation the Consumer Council for Water said it was extremely disappointed that Severn Trent Water had found yet more misreporting and overstating of data to the regulator.

"It is essential that all information which companies submit to Ofwat is accurate because levels of service, funding for future projects and the level of bills are shaped by it," a spokesman said.