It said the ‘deliberate and sophisticated financial reporting fraud’ at Austral, a civil, mining and marine contractor that contributes around 3% of group revenue, had resulted in overstated profits from 2019 onwards.

The impact of the fraud on historical operating profits is currently estimated to be £6m related to the first half of 2022, and £8m to £10m relating to prior years.

In a group profit warning, Michael Speakman, chief executive officer, said that an internal investigation is underway and Keller would be appointing an external adviser to undertake an independent investigation.

He said: “We have responded swiftly and decisively to a serious issue within one of our business units and a full investigation is underway.

“Until this process is complete and its consequences fully understood, it is inappropriate to comment further.

“The board and management team has taken, and will continue to take, all actions we think appropriate to ensure the maintenance of both high ethical and professional standards and resilient and effective controls throughout our organisation.”

Speakman added that while the fraud continued in the second half of 2022, and had impacted the board’s expectations for the 2022 full year results, Keller Group’s overall performance in the second half was strong.

Keller now expects to report a full-year operating profit slightly below the bottom end of the range of market expectations.

He added: “The group continues to perform well overall with the momentum achieved in the first half of the year continuing in the second half.”

Speakman said across the group Keller had benefitted from the actions taken to improve performance in North America foundations business. In Europe, trading remained robust in the second half, despite the operational challenges.

“Our substantial order book, together with the significant potential of the NEOM project in Saudi Arabia, support our confidence in the Keller’s prospects in both the short and medium term.”