In 2023–24, HMRC initiated compliance investigations in the majority of instances where it identified a risk of non-compliance.39 The average time it took HMRC to close an investigation increased each year over the period from 2018–19 to 2022–23 to a peak of 20 months, before falling to 14 months in 2023–24. For investigations which yielded more than £100,000, the average duration has continued to increase and is now 40 months.40 HMRC told us that the average duration of a case can be skewed, depending on which cases close during the year, and that there have been some particularly lengthy, long-running inquiries. It explained that the duration of a case can depend on the willingness of the customer and their agent to share information, and that taxpayers have the right to appeal to a tribunal against HMRC’s requests for information.41