Engineers worked around the clock to place 120 long beams to form the top of the box in just 14 days.

The lifting milestone paves the way for the vast box to be jacked 64m under the dual carriageway using a system designed by French contractor Fressynet.

The box will be jacked across on a guiding raft at a speed of up to 2.5 metres per hour.

A section of the A46 between Festival Island (Coventry) and Thickthorn Island (Kenilworth) will be closed for two weekends next month for the first stage of preparation work – with plans to move the structure into position during a full closure of the A46 Kenilworth Bypass in spring 2025 for up to three weeks.

John McNiffe, project director at BBV, said: “The safe and successful installation of 120 giant beams is another great achievement for the team who are delivering this box bridge slide in Warwickshire.

“The next stage includes construction of the deck and installation of the bridge parapets before the bridge can be moved into position under the existing carriageway, allowing HS2 trains to pass underneath.”

The structural design was carried out by Mott MacDonald and Systra JV.

Tim Akers, Engineering Manager for the Mott MacDonald SYSTRA Design Joint Venture, said: “We’re incredibly proud of the part we’ve played in the development of this structure.

“Through significant collaboration between HS2, National Highways and Balfour Beatty Vinci, the design has been reviewed and changed from a traditional ‘top down’ approach to an offline construction method with automated rapid and safe installation, reducing the impact to road users significantly.”