Construction can now start next year following the confirmation of both the independent investors to finance and deliver the scheme and contract agreements on the 24km tunnel drive under London.

The deals signed with Bazalgette Tunnel Limited, the consortium of investors that holds the concession for the project, paves the way for project to start.

Thames Water also announced that strong competition for both construction and financing has driven down costs for five million London bill payers.

At the peak of construction Thames Tideway will create more than 9,000 direct and indirect jobs around 24 sites in the capital.

For the East works package the Costain, VINCI Construction Grands Projets and Bachy Soletanche joint venture has signed off the contract at £605m, towards the lower end of the £500m-£800m estimate for this section.

Another three-way consortium consisting of Balfour Beatty, BAM Nuttall and Morgan Sindall has signed off the shorter western tunnel drive at a price of £416m, in the middlle of the £300m-£500m estimate.

A Ferrovial Agroman and Laing O’Rourke joint venture secured the largest central section drive for £746m, against a £600m-£900m estimate.

This morning Balfour Beatty said it would start mobilisation work for the 6km West tunnel project next month, with completion scheduled for 2022.

Leo Quinn, Balfour Beatty group chief executive said: “The award of this unique infrastructure project, which is part of the largest ever undertaken by the UK water industry, is another example of the part we are playing in 21^st Century engineering.”

The trio of winning consortia will drive the 7.2m diameter tunnel under much of the route of the Thames from Acton in West London to Abbey Mills in the east.

Innovative engineering in the design phase has already reduced the tunnel from the initial 32km proposed, and reduced the number of construction sites needed from 45 to 24.

The tunnels will be dug with a gently sloping gradient, falling 1m for every 790m it travels at a depth up to 60m below the surface.

(Click map to enlarge)

Thames Water also announced a much lower than predicted cost of the project to customers today.

The company’s current average household bill for water and wastewater of around £370 per year is now expected to remain at that level, before inflation, until at least 2020.

Martin Baggs, CEO of Thames Water, said: “It’s no exaggeration to say this is a truly momentous day for London and the River Thames. I want to thank everyone who has played a part in getting us this far.

“It’s a historic achievement and I look forward to supporting Bazalgette Tunnel Limited in ensuring the project is delivered safely, on time and to budget.

“The strong competition for both construction and financing has driven down costs for our more than five million bill payers.

“Our current annual bills already include £7 for the tunnel and this will eventually rise to a total of £20 to £25, before inflation.

He added: “This is sharply down from the original maximum estimate of £70 to £80 set four years ago.

“The really good news is that cheaper finance and other efficiencies mean that this hugely important piece of national infrastructure can be built while keeping our bills at or around their current level, before inflation, for at least the next five years.”