The section of the vital A4 arterial route in West of London was shut last year for urgency remedial works by Amey.

Now Costain will carry out extensive long term repairs under an ECI framework with Transport for London.

The damage to the ageing 1960s structure has been caused by water ingress, including salt water due to grit laid during the winter months, which has corroded and weakened supporting cables.

Andrew Wyllie, Chief Executive of Costain, said: “Costain is delighted to gain a place on TfL’s framework, and to commence work on the Hammersmith Flyover which is a technically challenging structure and an important part of London’s infrastructure.

“This award further enhances Costain’s reputation for innovation and engineering expertise across the whole life cycle of an infrastructure asset, as well as our recognised commitment to providing our customers with certainty of delivery and cost within a collaborative working approach.”

The full project scope will be defined during the ECI phase, but is likely to involve strengthening the flyover using post-tensioning, replacing bearings, waterproofing and resurfacing the deck, and replacing the drainage.

Hammersmith Flyover, which is used by 90,000 road users a day, is situated on one of London’s main strategic routes, and the strengthening work is essential to keep London moving.

The deal is part of a wider £200m ECI framework and a major programme of bridge and tunnel strengthening in the capital.

The four-year framework and the ECI work for Hammersmith will start immediately.