Super-sewer plans to improve the River Lee

The application also includes plans to extend Beckton Sewage Treatment Works in East London, which will enable the plant to treat larger volumes of wastewater to a higher quality.

The proposed Lee Tunnel, which will stretch 4.3 miles (6.9km) from Abbey Mills Pumping Station in Stratford to Beckton Sewage Treatment Works, will store and transfer dilute sewage which would otherwise be discharged into the river due to the original design of London's sewers. Built during the Victorian era, London's 'combined' sewerage system, which intakes both rainfall and sewage, was designed to overflow into the River Thames and its tributaries at times of high flow to prevent flooding of streets and homes.

The largest overflow point is at Abbey Mills Pumping Station, in Stratford, which discharges into the River Lee. This accounts for up to half of the total volume of effluent that is discharged from the most polluting overflows along the tidal Thames.

Steve Walker, Thames Water's Director of Major Projects, said: "Our proposals to build the Lee Tunnel and extend Beckton sewage treatment works are essential to prevent approximately 16 million cubic metres of diluted sewage entering the river each year. Not only is this harmful to the environment but it also impacts on people's enjoyment of the river. We will also be upgrading our processes at Beckton enabling the plant to meet new treatment standards.

"Population growth, development and climate change mean that sewer discharges will become more frequent over future years, and we must act now to provide our customers with a sewerage system fit for the 21st Century and beyond."

The Government announced its decision to support both the Lee Tunnel project and Thames Tunnel project in March 2007. Construction of the Lee Tunnel, in advance of the Thames Tunnel, will have environmental and operational benefits by capturing effluent from a single overflow point at Abbey Mills. Work is expected to start in 2009 once the relevant regulatory and planning approvals have been obtained. The tunnel is due for completion by 2014.

The Thames Tunnel, which is a much larger and more complex project, will run 20 miles (32km) from Hammersmith in the west, to Beckton in the east, and will prevent discharges from 34 overflow points along the Thames Tideway. Construction is expected to begin in 2012 with completion in 2020.

The Lee Tunnel and extension to Beckton Sewage Treatment Works is a separate, independent project, with the Lee Tunnel capable of being linked to the proposed Thames Tunnel.

The planning application for the Lee Tunnel and Beckton Sewage Treatment Works extension was submitted on 30 May to the London Borough of Newham, the London Thames Gateway Corporation and the Olympic Delivery Authority.