Underground construction of London’s Tideway sewer has been completed with the lifting of a 1,200-tonne lid to cap off the project’s deepest shaft.

The lifting of the 24m-wide concrete lid at Abbey Mills Pumping Station was undertaken yesterday by positioning a gantry crane on two self-propelled modular transporters and manoeuvring the structure in place. The operation in east London took five hours.

Tideway CEO Andy Mitchell said it was a moment all those working on the project had 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,” he said.

“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.”

The new super sewer comprises a 25km tunnel, two connection tunnels, 21 shafts, a host of valves and vortex generators.

The first sewage is expected to flow into the tunnel this summer and it should be fully operational in 2025. It will be operated by Thames Water.

In a typical year, around 40 million tonnes of storm sewage spills into the River Thames. The new tunnel will intercept, store and ultimately transfer sewage waste away from the River Thames.

Six TBMs were used on the project. Tunnelling was completed in April 2022 after four years of excavation.

With the cap now on the shaft at Abbey Mills, Tideway is continuing its architecture and landscaping works at various sites along the route of the tunnel, including Blackfriars, Victoria and Chelsea. These sites – seven in total – will soon new areas of public realm.