Construction work on the £15.9bn Crossrail link officially started at Canary Wharf on Friday.

Prime minister Gordon Brown and London mayor Boris Johnson attended the ceremony to mark the launch of laying the first of nearly 440 18.5m-tall steel piles. The new line, designed to link Maidenhead and Heathrow to the west of London with Kent and Essex in the east, is being constructed despite continued uncertainty over parts of the funding package.

The piles will be sunk into the floor using 10-storey high piling cranes and Giken piling machines. Workers from Laing O'Rourke's Expanded division will sink between five and six piles a day once a second Giken machine becomes operational.

All of Crossrail's major contracts on the scheme have been awarded to US firms, or US-led consortiums, with Bechtel being made project partner and Transcend, a joint venture between Aecom, CH2M Hill and Nichols Group, being awarded the programme partner job.

The 118km line is expected to complete in 2017.