The cost of the failings by Concentrix, which until last autumn administered HMRC’s tax credits system, has emerged in a report.

The US firm stopped or amended tax credits awards in 12% of cases investigated, and, of these, 32% were overturned after a mandatory reconsideration. It left HMRC with a compensation bill of £86,815 after a series of complaints by claimants.

In a report, HMRC’s Contract with Concentrix, the National Audit Office uncovered numerous failings in the deal, which the Revenue terminated last November.

HMRC had estimated that the planned three-year contract would save £1bn from …