Corporate Responsibility

London tideway improvements.

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The Victorians designed London’s sewerage system to overflow into the River Thames during periods of extreme weather when the sewers reached capacity. This was to prevent the flooding of homes and streets. The 150 year old system is struggling to cope with modern demands resulting in more frequent discharges of raw sewage into the River Thames – around once a week on average.


To address this problem we developed three major engineering schemes designed to improve water quality in the River Thames. We’ve already completed two of these schemes (the Lee Tunnel and upgrades to all our major sewage treatment works in London) and the third, the Thames Tideway Tunnel, is due to be completed in 2023.

Sewage works upgrades.

We’ve completed a £675m project to modernise and extend London's five major sewage treatment works - Beckton, Crossness, Mogden, Long Reach and Riverside. The five sites are some of the biggest in the UK and serve over 7.5m Londoners.

This major construction programme increased the amount of sewage the sites can treat by between 40 and 60 per cent. This significantly reduced untreated discharges of storm sewage to the River Thames after heavy rainfall.

Individually, just one of the five upgrades was as big as any ever carried out on a sewage treatment works in in the UK. Effectively, we constructed brand new sewage treatment works on existing sites. The use of offsite build techniques helped reduce construction time by around 50 per cent. At Beckton alone, this ‘flat packed’ construction saved over 100,000 hours and 60 workers on site, was more cost effective and most importantly safer than more traditional construction techniques.

The Lee Tunnel.

The Lee Tunnel is the first of two tunnels, which will collectively capture 39 million tonnes of sewage in a typical year from the 35 most polluting combined sewer overflows built by the Victorians.

The Lee Tunnel alone helps prevent more than 16 million tonnes of sewage mixed with rainwater from overflowing into the River Lee each year, through capturing it and transferring it to Beckton, which has been expanded by 60 per cent to enable it to deal with the increased volumes.

The £678m tunnel collects discharges from London’s largest combined sewer overflow at Abbey Mills situated in Stratford, which previously accounted for 40 per cent of the total overflows each year.

This project is the largest delivered by the UK’s privatised water industry and the tunnel is the deepest ever constructed under London. The 6.9km long and seven meter diameter tunnel runs beneath the London Borough of Newham, from Abbey Mills pumping station to Beckton sewage treatment works. It forms a key part of the biggest expansion of London’s sewerage network since the 1860s and will help transform the quality of the capital’s major rivers.


In February 2015 we celebrated the completion of the tunnelling work with a visit from His Royal Highness the Prince of Wales. Mayor of London, Boris Johnson MP officially opened the Lee Tunnel in January 2016.

Mr Johnson said: “This amazing new super sewer is providing the bold infrastructure needed to support the movements of our rapidly growing city. For years our historic Victorian systems have heaved at the seams, muddling along, battling to cope with the increasing rainfall and waste of a modern population. Now the River Thames will benefit from vast improvements to its water quality with less pollution and overflow. Alongside my sustainable drainage work to reduce flooding, the investment in the Lee and the forthcoming Thames Tideway Tunnel are set to benefit Londoners for generations to come.”

Thames Tideway Tunnel.

The Thames Tideway Tunnel (TTT) is the second of two major new tunnels designed together to capture sewage from the 35 most polluting combined sewer overflows built by the Victorians. By 2023, when it is due for completion, the TTT in conjunction with the Lee tunnel and upgraded treatment sites, will make a significant difference to the health of the tidal River Thames.

Bazalgette Tunnel Limited, known to the public as ‘Tideway’, is the licensed infrastructure provider set up to finance, build, maintain and operate the Thames Tideway Tunnel.

The tunnel will be 25km long sewer, more than 7m in diameter and run up to 65m deep beneath the River Thames in London. It will connect to the combined sewer overflows (CSOs) located along the river banks and collect nearly all of the 18 million tonnes of sewage that pollutes the tidal River Thames in a typical year. The tunnel will transfer the sewage to Beckton sewage works in East London to be treated and returned safely back into the environment.

Tideway has now started main construction work, which is due to take seven years to complete. The tunnel will be a fantastic example of world leading British engineering at its best, and is expected to create more than 9,000 skilled jobs and make the River Thames cleaner for those that live, work and visit it.