London’s ‘super sewer’ to face NAO funding probe : The National Audit Office is to launch an investigation into London’s new Thames Tideway Tunnel, nicknamed the ‘super sewer’, over concerns about the project’s structural impact and its funding model, which has been described as ‘unusual’.

The 25km tunnel is to run underneath the Thames, and construction was due to start in the next few months. Tideway, a new company set up by Thames Water to deliver the scheme, will work with the government on the project, which is set to be one of the country’s largest infrastructure projects to date.

The system’s designers claim that it is an essential upgrade to the city’s elderly sewage system, which has not bee substantially improved upon since it was build in 1858. It is also intended to mitigate the tens of millions of tonnes of raw sewage which currently flows into the Thames every year.

That said, the project is not without significant risks, including the possible flooding of the London Underground, and undermining the foundations of Big Ben.

The NAO is therefore investigating why this particular solution to the sewage system has been chosen over several other less expensive and more environmentally friendly options. According to an NAO briefing note, the report will set out the risks faced by customers and taxpayers as the project moves towards completion, and how these risks are being mitigated.

Particularly under scrutiny is the scheme’s complex funding model, which aims to see water consumers pay for a third of construction costs via increased water utility bills. Taxpayers will shoulder the burden of any additional costs, such as overrunning construction work or global financial crises.

The Tideway is also being financed by a variety of investors, including German insurance group Allianz, which will provide £3billion of the total cost.

The report will be published in the autumn, when construction is currently due to start.

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