The first transmission circuits in south London’s £1bn electricity revamp have been turned on between Hurst substation and Crayford.

The 2.5km circuit uses a new high voltage 275kV network that runs through a tunnel route averaging 35 metres below ground, which was completed by ‘Christine the tunnel boring machine’ last year.

London Power Tunnels is a project started by National Grid in 2011 to reinforce the electricity transmission network in the capital by constructing more than 60km of new deep-level tunnels carrying high-voltage cables.

The new network of tunnels replaces a series of ageing power cables, most of which were buried directly beneath roads. These were becoming unreliable and difficult to maintain without disrupting traffic, and were unable to meet future demand for electricity. The new tunnels allow the power cables to be upgraded and maintained without disruption to traffic and residents on the surface.

The previous cables between Hurst and Crayford were reaching the end...