The FRC launched a probe into KPMG’s auditing of Carillion’s books when the contractor collapsed in January 2018.

In an update the FRC said: “The scale and complexity of this case is exceptional, with a huge volume of documents and information that has had to be reviewed and analysed.

“The investigation encompasses a four-year period, and numerous significant audit areas, including the accounting for construction and services contracts, pensions liabilities, goodwill and going concern.

“All of the accounting years and each of the audit areas identified remain under active consideration.

“The FRC therefore currently expects to complete the first stage of its investigation by summer 2020, rather than by January 2020.”

The FRC is also investigating the conduct of former Carillion directors Richard Adam and Zafar Khan.