A multi-million pound dig that will link Wimbledon to North London with a 20-mile tunnel has begun.

National Grid’s £773m London power tunnels scheme will dig deep under the capital, from Hackney to Wimbledon, to allow the installation of new electricity cables set to last more than 50 years.

Work on the 7.4-mile Wimbledon to Kensal Green stretch of the network is set to start next year and finish in 2018 – but is well under way on the first stretch in North London.

At a former clothes factory and carpet centre near Manor House station, a 127m tunnel-boring machine – named Cleopatra by schoolchildren – is slowly being built in a 6m-wide tunnel deep underground.

Project manager Mat Ray said: “London’s electricity demand is increasing by 3 per cent a year – that is mainly from businesses installing air-conditioning and using electricity for heating.

“Most of the current cables used in London were laid just under the surface in the 1950s and they are not going to have the capacity for the future.”

The machine will bore 120m each week, at depths of 12m to 60m, with workers building a ring of concrete slabs behind it – each one weighing three tonnes and making up the bulk of the cost of the project.

The clay already dug from the shaft has been used to finish landscaping at the Olympic site in east London.

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