The Enquirer can reveal five road bridges are now known to be suffering from defective welding in addition to the nine bridge structures impacted on HS2.

While both HS2 and National Highways are refusing to name the specific bridges and structures impacted, weight restrictions have been applied to several affected roads bridges while investigations and testing take place.

A National Highways spokesperson said: “We are carrying out targeted inspections on a small number of bridges to rule out any potential issues.

“These bridges remain safe to use. For any abnormal load movements, we have put restrictions in place as a precaution while we assess whether any further strengthening measures may be required.”

CGI of finished Birmingham approach viaduct and the steel support tripods

On HS2, the problem steelwork is clustered mainly on the key main approach viaducts to the flagship Curzon Street station in Birmingham. These are still under construction.

They are being delivered by main works contractor Balfour Beatty Vinci joint venture using Severfield to deliver corten steel structures, some of which are also due to be delivered by Portuguese steelwork specialist Martifer, which is not implicated in quality concerns.

Three of the nine affected bridges built for HS2 – two rail bridges and one road bridge – are currently in use.

Completed HS2 viaducts impacted

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Duddeston Mill Road bridge, Birmingham – main works contractor BBV

Princes Risborough to Aylesbury rail bridge in Buckinghamshire which Carries Chiltern main line over HS2 – EKFB

Chiltern Line bridge in Buckinghamshire

Harvil Road bridge, Hillingdon. Road bridge over Chiltern Line for main works contractor SCS.

It is understood that the spotlight is on the integrity of client-specified full penetration butt welds on fabricated steelwork.

It is also believed the material impacted is weathering Corten steel which requires specialist welding wire or gas.

BBV is now understood to be seeking to employ a third-party firm to provide welding inspections for the both factory and onsite fabrication of key steel structures as part of the HS2 Curzon Approach Viaducts project moving forward.

The assets to be inspected going into construction are Saltley Canal Under Bridge, Lawley Middleway and Curzon 3 Tripods, supplied by Severfield UK and the Duddeston Junction Viaduct and Curzon 2 section to be supplied by Martifer.

So far Severfield has spent £7.1m on testing and remedial works and expects to incur a further £13.3m cost on eight of the projects.

Severfield added that it still needed to agree solutions on four of the remaining structures where weld testing is ongoing.

Yesterday Severfield said it would be pursuing all potential recoveries from third parties, including insurance.