Main contractor's notification of a defect to a subcontractor

We are the subcontractor to the main contractor on a highways project under NEC4 option B, the works are complete and the client has notified a defect to the main contractor which they believe is our liability.

The defect notified is that a bridge expansion joint is leaking water from the road surface to the structure below and insinuate that this is our responsibility, however our site teams and operations manager believe that this is due to the design of the joint itself and not the installation. We do not have any design liability under this contract and we have photographic records that we have completed the works as per the work information. We do not have a collateral warranty to the client, but the works are still within the defects period.

My question is, what is our best recourse for this? and how should we approach challenging the main contractor and client? - The main contractor wants us to speak directly with the client regarding the issue.

It would be sensible to have a triparty meeting to discuss the issue and for you to explain your view to the Contractor and Client. If there is still a difference of opinion then it would be sensible for a joint survey to be carried out to ascertain the cause of the “leak” and hence the responsibility.