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Wednesday, 31 August 2016 08:23

Government spending watchdog to investigate Thames Tideway Tunnel assurance arrangements

The National Audit Office, the government’s spending watchdog, has launched an investigation into the assurance arrangements for the £4.2 billion Thames Tideway Tunnel – the NAO will publish its report in the autumn.

It 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 the risks are being mitigated.

The investigation is a follow-up to the NAO’s 2014 report, Thames Tideway Tunnel: early review of potential risks to value for money. At the time of the report  £1.4 billion of the planned £4.2 billion cost was expected to be spent by Thames Water on the project, with the remaining £2.8 billion expected to be spent by an ‘infrastructure provider’, independent of Thames Water (2013 estimate in 2011 prices).

 The 2014 report explained the roles of the different parties, identified potential risks to value for money and set out what the NAO expected good project management to look like. To avoid influencing the outcome of ongoing competitions for the construction and financing of the project, it did not evaluate the value for money of the project.

Announcing the new investigation, the NAO said:

“Unusually for the privatised English and Welsh water sector, it is being delivered by a specially created company, and benefits from a contingent support package provided by government in its construction phase.”

Interested parties who would like to provide evidence for the investigation should email the study team on This e-mail address is being protected from spambots. You need JavaScript enabled to view it , putting the study title Investigation into assurance arrangements over the Thames Tideway Tunnel in the subject line. The team will consider all evidence provided - however, the NAO said that due to the volume of information received it may not respond directly. 

Click here to download the 2014 report , Thames Tideway Tunnel: early review of potential risks to value for money

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