The three-year project involved a tunnel boring machine, known locally as ‘Dora the Bora’, constructing a 3.2 km, 2.8 m diameter sewer to carry excess rainwater and sewage during storms. This will prevent flows backing up into streets and properties in West Ham.

Dora took seven months to bore through 70,000 tonnes of earth, 20 m below London.

Also included in the project was the construction of a new sewage pumping station at Abbey Mills in east London, as well as 5.6 km of sewers linking to the main sewer tunnel.

Head of Capital Delivery for Thames Water Lawrence Gosden said “Protecting customers from the misery of sewer flooding is a top priority for us. No one should have to put up with this truly horrible experience.”

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Aecom designed the project, while UK engineering firm Costain was contracted to construct the sewer.

Meanwhile, Black & Veatch has been awarded a £100 million contract to carry out improvements to Thames Water’s infrastructure.

This is the final ‘base load’ contract within the recently announced £5 billion upgrade to London’s ageing underground infrastructure. Contracts have also been awarded to Optimise, MGJV and GBM.

Thames Water Chief Executive Martin Baggs said "“We've challenged all our contractors to deliver the best possible value for our £13.6 million customers' money. Instead of letting lots of small contracts to multiple contractors, we're working with a select group of leading organisations to deliver the base load of our five-year investment program.”

The planned works include replacing Victorian-era water mains, upgrading sewers to protect customer homes from flooding, improving the water and sewage treatment works, and extending water and sewerage networks to accommodate future population growth.