A utility company has admitted plans to improve its wastewater disposal system would lead to raw sewage being flushed onto a beach.

Southern Water has announced it intends to build an overflow pipe which would release untreated waste into the sea at Black Rock, Brighton, as part of its £200 million waste treatment project at Peacehaven.

The company says the pipe, opposite the Volks Electric Railway in Madeira Drive, would only be operated during extreme storms.

It says the contingency plan is the only way to protect homes in central Brighton and those towards Patcham from flooding - and the amount of sewage would be negligible.

But environment group Surfers Against Sewage (SAS) has mounted a campaign for supporters to lobby the Environment Agency against giving the company permission because of public health and water quality considerations.

SAS campaigns director Richard Hardy said: "We are concerned about the impact it will have on the surf break and on the marina. When you get untreated sewage going into an area beside bathers and other recreational water users it poses significant risks."

SAS records claim that people who have been in contact with sewage-polluted water have suffered nose and throat infections, gastroenteritis and more more serious ailments including hepatitis A and septicaemia.

Regular beach user David Morris, 80, of Lewes Crescent, Brighton, complained that Southern Water had no way of knowing how often it would be required.

He added: "I remember Michael Fish saying there was not going to be a hurricane and five hours later there was."

A Southern Water spokesman said the emergency release could not be sited further out at sea because the excess water would have to be drained immediately.

He said the amount of untreated sewage would be "negligible" as it would be diluted with high volumes of rain water and there would be no health risks. The overflow pipe is part of a project to improve treatment of the 95 million litres of waste produced daily by Brighton and Hove and surrounding areas.

The spokesman said: "On very rare occasions we'll get very heavy rainfall so water would come out into people's homes. This is something we must guard against and the way to do this it to have an emergency release point in the system, which is what we're doing at Black Rock."