Top secret £42m super-tunnel to power US embassy

A secret tunnel more than 70ft below the streets of London will provide high-security power to the American Embassy.

When complete this summer, cables threaded through the £42 million project will also electrify Battersea Power Station and tens of thousands of homes in the 560-acre Nine Elms development.

Extra supply is needed as London’s future power needs rocket with the advent of electric cars, said UK Power Networks, the infrastructure giant behind the works.

The exact location of the 8.5km (5.3-mile) tunnel near the river must remain under wraps for “security reasons”. Its depth ranges from 72ft (22m) to 98ft (30m) depending on the location of old gas pipes, rail tracks and sewers criss-crossing around it.

The two-year project included digging a 108ft (330m) spur, known as the Battersea Cable Tunnel, that breaks into the existing main bore. The spur was drilled out using a tunnel-boring machine, which heaved concrete reinforcement panels into the clay as it went.

A junction chamber linking the spur to the main tunnel was dug by hand using techniques from the time of Victorian engineer Isambard Kingdom Brunel, but with modern pneumatic shovels.

Much of the digging was done while 132,000-volt cables were live in the existing main tunnel, which are about 500 times more dangerous than a domestic plug.

Rosie Bridger, project manager for UK Power Networks, said: “As London grows, demand continues to increase, and working in central London space is tight.

“One of the biggest challenges on this project is that we’ve got to maintain security of supply to our London customers.”