A company that wants to build an offshore sewage plant has objected to a water firm's plans to develop a greenfield site.

Kaiak is trying to persuade Southern Water to drop the idea of building a wastewater treatment works in Peacehaven, east of Brighton.

Instead it wants the company to back its proposal to build an island made of reclaimed land off Black Rock, next to Brighton Marina.

Kaiak, based in Swansea, said a sewage works could be stored inside the island, leaving space on top for buildings like a hotel, a gallery or a restaurant.

The technique, known as Starfish, would create a 5.4 acre platform level with the height of the breakwater.

Kaiak presented the proposal to Southern Water in 2003.

The construction firm has now filed formal objections to East Sussex County Council and Brighton and Hove City Council, the two councils considering Southern Water's planning application for the £200 million works.

Kaiak claims its proposal is a better environmental option and would require less tunnelling in the community.

Gerald Clark, Kaiak president, said: "The Starfish modular approach will deliver a simpler, more sustainable and straightforward solution to the one presently on offer."

An East Sussex County Council spokeswoman said: "A letter has been received from Kaiak. Its objections will be considered as part of the planning decision process.

"A report will be made to the planning committee about the application in November at the earliest."

A Southern Water spokeswoman said the idea of an offshore facility had been considered and rejected because the coastline between Brighton Marina and Newhaven was a Site of Special Scientific Interest and there was a proposal to extend this into the sea.

She said: "The operational and health and safety issues associated with offshore treatment location are also significant. Access for operators, maintenance staff, replacement of plant and equipment, deliveries and removals would need to be available at all times. Given the tidal range, currents and sea states possible in the area it is considered that a land bridge or a major tunnel would be required."