London super sewer: Everything you need to know about the new £5bn Thames Tideway Tunnel

Work to build London’s £5bn super sewer, including its tunnels and shafts, is now fully complete after eight years of construction.

To mark the construction of the tunnel being completed, a 1,200 tonne concrete lid was lifted onto a shaft in Stratford on Wednesday (March 27).

What is the Thames Tideway Tunnel?

The super sewer, also known as the Thames Tideway Tunnel, has been designed to reduce sewage pollution in the central London River Thames.

The 16 mile (25km) long pipe will divert 34 of the most polluting sewage outflows (CSO's) that have been discharging into the river.

The entire tunnel includes a 7.2m-wide main tunnel, a 4.5km connection tunnel in south-east London, and a 1.1km tunnel in south-west London. 

In a typical year, tens of millions of tonnes of storm sewage spill into the River Thames, said Tideway. Once fully operational, the new infrastructure will reduce those spills almost completely.

The first sewage is expected to flow into the tunnel this summer and it should be fully operational in 2025. Initially expected to cost £4.2bn, the tunnel has ended up costing about £5bn. 

That cost will be paid for by Thames Water customers over several decades with bills increasing by about £25 a year.

What is Tideway saying?

Tideway CEO Andy Mitchell said: “This is the moment we’ve all been waiting for. The underground civil engineering on the Tideway project is now complete following eight years of dedicated hard work from all our teams working in the capital.  

“There is still work to do – we need to finish some above-ground structures and, crucially, test the system – but this nonetheless marks an absolutely critical milestone for the Tideway project and for London.”

What are critics saying?

Critics say with climate change the tunnel may have a limited lifespan. This is due to a predicted increase in rainfall to the UK, meaning there will be times when even the huge super sewer fills up.

"The super sewer is a massive, expensive pipe and I think the Victorians would be a bit embarrassed that we haven't come up with a more modern solution than that," Theo Thomas from campaign group London Waterkeeper told the BBC.

Mr Thomas would rather the money had been spent right across London on projects that stopped rain flowing directly into drains where it mixes with raw sewage.

"You could use nature to be dealing with this. You could have lots of areas that would soak up the rain rather than rush it off the streets and rush it off the roofs straight into the sewers."