Press release

Environment secretary Caroline Spelman supports Thames tunnel plans

Environment Secretary Caroline Spelman today gave her support to Thames Water's plans for a tunnel to reduce the amount of raw sewage discharged into the River Thames.

This was published under the 2010 to 2015 Conservative and Liberal Democrat coalition government

The core of London’s sewage network was designed in the late 19th Century and was designed to overflow at times of heavy rainfall to ensure that sewage did not back up into houses and streets. Combined Sewer Overflows (CSOs) were intended to discharge the raw sewage into the Thames in the event of extremely heavy rain.

Increasing populations and changes to land use in London have lead to this occurring around 50 times per year. With further population growth and projected climate change, this figure is expected to increase in coming decades and spills could occur when there is very little rain. This also creates problems for the UK’s continued compliance with EU waste water treatment regulations.

On 22 March 2007, the then Minister for Climate Change and the Environment announced his support for a tunnel based solution to the problems in the Thames and asked Thames Water to take forward the design process for the Thames Tideway Project. This included the Lee Tunnel (a smaller tunnel on which construction work has begun), upgrades to sewage treatment works and the larger Thames Tunnel. In the intervening years Thames Water, the Environment Agency and Ofwat have worked together researching and analysing different options. Thames Water estimates that the proposed Tunnel will cost £3.6bn which could result in bill increases of around £60-65 per year for Thames Water customers.

Caroline Spelman said:

‘A tunnel continues to offer by far the most cost effective solution to the unacceptable problem of raw sewage being regularly discharged into the Thames. This is a large and complex project and I recognise that it comes at a significant cost. I will ensure that Defra and Ofwat continue to scrutinise the costs and options to ensure that Thames Water’s proposals represent proper value for money.’

Thames Water will shortly launch a consultation exercise on the need for the tunnel, the route and the sites needed to construct and operate the project. Defra carried out an Impact Assessment in 2007 and will update this before publishing the revised version of the document on the Defra website.


Sewage collection and treatment in the UK is largely determined by the requirements of the Urban Waste Water Treatment Directive (91/271/EEC) transposed into domestic law by the Urban Waste Water Treatment (England and Wales) Regulations 1994.

The controlled use of CSOs is a necessary part of combined sewer systems that collect both rainwater and sewage. Without them, sewer flooding of premises and roads and overloading of sewage treatment works could occur following heavy rainfall.

Recent investigations have shown that around 39 million cubic metres of storm water are discharged annually from the tideway CSOs with six of those 57 CSOs discharging on a weekly basis (50 - 60 times annually).

Currently under construction is the Lee Tunnel which runs from Abbey Mills pumping station to Beckton STW and will be completed in 2014. The Lee Tunnel and Beckton STW upgrade will reduce the total volume of discharges to the tideway by around two thirds. The Thames Tunnel is expected to be completed in 2020.

A separate consultation on the route of the Thames Tunnel is being carried out by Thames Water during September 2010.

Further information on the Tunnel can be found on the Defra website at

Written ministerial statement - Sewer overflows (River Thames)

In the 19th century Sir Joseph Bazalgette built a sewerage network for London with the capacity that he believed would meet all foreseeable needs. It has been updated and modernised but for some years has been coming under increased strain to the point that combined sewer overflows discharge raw sewage into the River Thames on around 50 occasions a year.

This figure is expected to increase. Recent Thames Water work has shown that the system is operating closer to its maximum capacity than previously recognised and, with population growth, increasing urbanisation and climate change, it is estimated that in ten to twenty years time sewage will be overflowing into the Thames even when there is little rain.

Complete eradication of some spills of sewage into the Thames during periods of heavy rainfall is not feasible: this is the legacy of a sewerage system which carries both foul water and rainwater. But the frequency and volume of spills we face in future is unacceptable and should be reduced to ensure that environmental standards in the Thames continue to meet the standards set by the Urban Waste ?Water Treatment (England and Wales) Regulations 1994.

Since the 22nd March 2007 statement by the then Minister for Climate Change and the Environment, Ian Pearson, on the need to improve the water quality in the Thames by upgrading the sewerage infrastructure, Thames Water have started work on building a tunnel (known as the Lee tunnel) from Abbey Mills pumping station to an upgraded Beckton Sewage Treatment works at a total cost of around £0.8bn. When complete these works should reduce the total volume of sewage overflows into the tidal Thames by around two thirds. However significant volumes of raw sewage will still continue to enter the Thames at times of heavy rainfall particularly in the higher reaches of the tidal Thames from Hammersmith through central London which will get less benefit from the Lee Tunnel.

Ian Pearson’s statement supported the construction of a second ‘Thames Tunnel’ to address unsatisfactory overflows from Hammersmith to Beckton. Since 2007 Thames Water, the Environment Agency, and Ofwat have worked together to improve the evidence base, to take forward the design process including costings, and explore possible commercial arrangements. The then Government announced its intention to go forward with the scheme. Despite that the European Commission has continued to pursue infractions proceedings against us claiming we are failing to meet our obligations under the Urban Waste Water Treatment Directive in the London area, and in Whitburn in the North East of England.

In 2007 the then Government judged the cost of the scheme to be at least £2 billion, with a peak annual increase in bills for Thames Water customers of £37.Since then greater analysis and study by Thames Water have led to a revised estimate of £3.6bn, including contingency costs but excluding the Lee Tunnel and other elements of the scheme which have already been contracted for. This could result in future peak annual bill increases of around £60-65 (£80-90 including the Lee Tunnel and other elements).

I recognise that in the current economic context this represents a significant cost to Thames Water customers and, while we judge this to be a robust cost estimate for this stage of the process we cannot rule out further changes to the estimates as work progresses. However a Thames Tunnel continues to offer (by far) the lowest cost solution to the problem and I believe Thames Water should continue to press forward with this project working with Ofwat, the Environment Agency and Defra on the regulatory, commercial and planning processes. Thames Water intend to consult on options for the route of the Tunnel shortly. We with Ofwat will continue to ensure that the costs are scrutinised and reviewed so that I can be assured before Thames Water sign a construction contract that the final proposal represents proper value for money. As we go through this process I intend to update the 2007 Impact Assessment for the Tunnel and place it on the Defra website.

I am also minded that development consent for the project should be dealt with under the regime for nationally significant infrastructure projects established by the Planning Act 2008. I consider that this project, with its unique scale and complexity, is of national significance, and therefore appropriate for this regime.

I will be considering the appropriate mechanism under the 2008 Act to ensure the Thames Tunnel project is considered under this national level regime and intend to include consideration of the Thames Tunnel in the draft National Policy Statement for waste water. I plan to lay this before both Houses of Parliament later this autumn.

Published 7 September 2010