Inside London's hidden power tunnels

A network of power tunnels are being created deep under London's streets to improve the resilience of the capital's power supply as the city's population continues to grow.

Costing about £1bn, the latest one is 20 miles (32km) long and has been bored under south London.

BBC London's Tom Edwards has been to have a look.

Filming by David Perella. Edited by Sarah Lee.