A water company has come under increased pressure to give full refunds to customers who have been charged for a service they never received.

The Argus revealed in May how Southern Water had charged its 593,000 Sussex customers about £18 a year since 1989 for draining water that falls on people's homes.

A high proportion of them do not use the service as the water simply drains into soakaway systems and does not reach the public sewer.

But all of them have been charged and more than 470 have written to Ronnie Mercer, the company's managing director, demanding full refunds after the Argus launched its Money Down the Drain campaign. The letters were delivered to the firm's Worthing headquarters by David Lepper MP last month.

Although the company is urging effected customers to apply for refunds, it is refusing to make them retrospectively.

The charging was revealed after industry regulator Ofwat ordered water companies in England and Wales to give customers a breakdown of their bills.

The Argus has now learned that Severn Trent Water has told customers about the charges since 1984 and inviting them to apply for refunds.

North West Water has been doing the same thing since 1997.

A Severn Trent Water spokesman said: "We have always believed it is important for our customers to know what they are paying for.

"If they are not getting a service from us then they should be aware because we would not want to charge them for it."

Mr Lepper said he would be seeking another meeting with Mr Mercer, adding: "During my last meeting I was given assurances that Southern Water was at the forefront of water companies responding to Ofwat's guidance.

"But the fact other companies have been completely transparent much earlier and without prompting does make me look at this issue in another light.

"I feel I have been a little bit misled by Southern Water over this and hope they will look at what some of the other water companies have been doing and rethink."

A Southern Water spokeswoman said: "This is a small part of our business overall. What other companies have done in the past is not something we can comment on."