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New time-lapse footage has been released showing the progress being made below the capital on Crossrail.
More than five and a half miles of underground tunnels have now been dug.
These pictures show the work that is being carried out at the sites of Finsbury Circus and the new Liverpool Street Station.
The first Crossrail trains are due to run in 2018.
Crossrail - the high speed commuter line that will cut under London's underground stations - was almost a casualty of the Coalition spending cuts, but the Mayor of London has now unveiled the first of two tunnelling machines that will drill the gigantic holes through the capital.
London Mayor Boris Johnson and Transport Minister Justine Greening talked to London Tonight about Crossrail.
Europe's largest construction project is about to become reality after decades of dithering, false starts and cancellation. Crossrail - a new high speed commuter line under central London - will take over from the Olympics as the capital's "next big thing".
The 73-mile route will link Maidenhead and Heathrow in the west to Shenfield and Abbey Wood in the East. The first of six tunnelling machines has been unveiled at Westbourne Park, close to the western portal of the Crossail tunnels at Paddington.
The machine will begin drilling in about a week's time and should reach Farringdon by late 2013. A mainline railway running beneath the capital was first conceived by the Victorian engineer Isambard Brunel.
A more modern version was cancelled by the Conservative government in the 1990s but was revived under Tony Blair.
The project appeared in doubt once again in 2010 when the incoming coalition government drew up a list of spending cuts but the new line finally got the go-ahead in the Comprehensive Spending Review.
A series of cost-cutting measures has reduced the price from £15.9bn to £14.8bn but Crossrail will now open in 2018 instead of 2017.