We asked HMRC why it had taken longer and was costing more to remediate its legacy systems. HMRC said that some of the systems had proved more complex than expected and it had underestimated costs.45 Progress had also been slowed by HMRC transferring some funding for one of its remediation programmes in 2023–24 to higher priorities.46 We asked HMRC whether it now understands what more it needs to do, what it will cost and when it expects remediation to be complete. HMRC said that it had a good understanding of what it needed to do and had a plan. But it was unable to say when it would complete remediation because funding for the three years after 2025–26 would not be known until it had its spending review settlement in June 2025.47