The National Audit Office (NAO) said the investigation is a follow-up to its 2014 report – Thames Tideway Tunnel: early review of potential risks to value for money – and will examine how the project’s public sector steering group gained assurance over the evidence base which informed the target outcome for the project and the choice of the tunnel over alternative options.
It will also set out the risks faced by customers and taxpayers as the project moves towards completion, and how these risks are being mitigated.
The Tideway underground sewer is intended to reduce the volume of spills from London’s sewers into the tidal part of the Thames, and therefore achieve compliance with the Urban Waste Water Treatment Directive. It is being delivered by Bazalgette Tunnel, as infrastructure provider.