London's unknown 'tunnelling revival'
London is at the beginning of a tunnelling revival, say experts.
One project, called the London Power Tunnels, has been burrowing away beneath the streets of the capital for 18 months.
John Trounson, of National Grid, says cables are increasingly being laid in tunnels to avoid disruption.
Crossrail chairman Terry Morgan said he believes the rail project and its supply chain will bring 50 to 60,000 jobs over the next two years.
BBC London's Environment Correspondent, Tom Edwards, was given exclusive access.