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Crossrail: A rare look deep under London

25 January 2013 Last updated at 14:33 GMT

The £15bn Crossrail project - linking Shenfield in Essex to Maidenhead in Berkshire via London - is the largest engineering project in Europe.

So far, two of the 26 miles of tunnel have been bored and BBC London's transport correspondent Tom Edwards is the first to be allowed to film deep under west London.