Crossrail tunnels
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Beneath London in Crossrail's tunnels

25 April 2014 Last updated at 20:53 BST

Crossrail is Europe's biggest infrastructure project and is planned to run from Reading and Heathrow Airport, west of London, to Abbey Wood and Shenfield in the east by 2018.

The latest work has involved digging deep beneath Stepney, in east London, where the eastern end of the line will split into two - heading onto south east London and Essex.

BBC London's Alice Bhandhukravi reports from inside the tunnels.