Tilbury Douglas has failed in a legal claim that Arup should pay it £6m because of defective designs at a mixed-use development in Edinburgh.

The contractor had alleged that Arup produced designs that were “incapable of implementation” on the revamp of the former Haymarket railway yard in central Edinburgh.

But Court of Session inner house judge Lord Malcolm rejected the claim because it was lodged too late.

In 2012, Tilbury Douglas, then called Interserve, formed a development joint venture with Tiger Developments, and Interserve became principal contractor, overseeing enabling works for five mixed-use buildings that would include office, retail and hotel space.

Tilbury Douglas appointed Arup to deliver civil and structural engineering services for the enabling works, including a designs for the tunnels.

Arup’s design included reinforcement of the northern tunnel brickwork with stitch grouting to cut the risk of the brickwork collapsing once the top of the tunnel, known as the overburden, was removed.

Bam Nuttall was appointed to carry out the enabling works, but soon reported concerns about the safety of that section of brickwork.

Studies by Bam and then Arup confirmed repairs to the brickwork were needed, including grouting the entire tunnel and fixing voids running the length of the northern wall.

Tilbury Douglas told the court that Arup’s design did not take account of the likely presence of voids within and behind the lining of the north tunnel, and failed to make allowance for the annular and interstitial grouting that would be required as a result. It argued Arup owed it £6m to cover necessary repairs and delays to the job.

By June 2014, the enabling works were delayed by six weeks, while Bam sought more than £1m for the extra work.

Tilbury Douglas argued that Arup had “erroneous and overly optimistic assumptions” about the strength of the wall before it started its work.

“Arup produced a design which failed to reflect accurately the physical conditions of the site and which was therefore incapable of implementation,” Tilbury Douglas said.

The contractor argued that Arup breached its contract and “failed to exercise the skill, care and diligence expected of a competent civil and structural engineer” – thereby causing the delay and extra costs.

A court initially said the case was able to proceed, but the claim has now been thrown out because Tilbury Douglas only registered it in July 2019, more than five years after the issues became apparent.

Tilbury Douglas had argued that it only registered the claim eight months late because Arup had assured it there were no problems in the structure, a point on which the first judge agreed and said the case could go ahead.

But Lord Malcolm ruled the previous judge had “erred in his reasoning”.

Instead, Lord Malcolm ruled Arup was simply “expressing confidence in their design”, and that “it was up to Tilbury whether to accept those assurances, or at least not question them”.

“In the absence of proof of an error, it is difficult to elaborate on how reasonable diligence might have avoided or corrected it [Arup’s alleged mistakes],” he said.

“On the assumption that the design was deficient, had Tilbury seen a need to explore the issue, on the face of it there was more than enough to alert those involved to the need to be less accepting of Arup’s statements.”