HMRC handles large sums of money, both collecting and paying out.68 It relies on financial estimates in various different contexts to help achieve its objectives. Yet we have recently seen several examples where there have been mistakes in those estimates. We asked the Department about the circumstances of its breach by £726 million, in 2019–20, of its net cash requirement total, an important parliamentary control over public spending. The Comptroller and Auditor General had to qualify his opinion on HMRC’s accounts because of this breach. HMRC recognised the seriousness of its breach. It explained that it had made an error in calculating its cash requirement which meant that it used more cash than it had predicted. The Department noted that it had not exceeded its budget and that in its view “there was no real-world impact from this error”. As a result of the breach, HMRC commissioned a review by its internal audit function to understand what had gone wrong and identify improvements to its processes for estimating its cash requirements.69 In a separate example, HMRC, as explained in its own Annual Report and Accounts, also had to correct its estimates of Corporation Tax revenues by some £6.6 billion in 2019–20, as a result of errors it made in its estimates in previous years.70