A field in Eltham has played host to a major milestone in a billion-pound project to make sure the capital’s lights stay on – with a tunnelling machine breaking through after a seven-mile trip across southeast London.

Grace, a 140-tonne machine, arrived at Falconwood Field on Saturday as part of National Grid’s London Power Tunnels project, which involves building 20 miles of tunnels under the capital to boost the electricity system’s resilience as demand grows.

The machine’s appearance at the worksite off Welling Way marks the end of tunnelling on the project. Grace had travelled from a substation in the Old Kent Road gasworks, and the tunnel will now be fitted with high-voltage cables. 

Other tunnels link the Old Kent Road site with Wimbledon and the Hurst substation in countryside near Bexley, while a fourth tunnel runs from Hurst to Crayford. The tunnels are up to 60 metres deep, and when completed will carry 125 miles of cables.

In total the project, which began in March 2020, will have shifted 900,000 tonnes of earth – equivalent in volume to half of Wembley Stadium.

Work is due to be finished by 2026. Alice Delahunty, the president of National Grid Transmission, said: “Our London Power Tunnels project has achieved a lot since it kicked off in 2020, but the final tunnelling breakthrough at Eltham is a particularly remarkable moment.

“This complex engineering endeavour is now really taking shape, with completion of tunnelling now physically linking our sites across South London for the first time and meaning we can move on to the next chapter to progress our vital cabling work.

“The outstanding effort by our project teams and suppliers is strengthening London’s electricity network and making sure it safely, reliably and efficiently powers homes and businesses in the capital for years to come.”