Poor design and testing of OSCAR II caused significant delays to the Whole of Government Accounts. In July 2020 the Treasury replaced its now obsolete IT system with a new system, OSCAR II, used for collecting and consolidating data from component bodies into the WGA. This update was expected to bring significant benefits including increased efficiencies, improved data collection and analysis and to lead to advancements in the quality of information in the WGA. However, the Treasury failed to anticipate a number of significant problems that arose during implementation which the Treasury estimates contributed to the delays to delivery by an estimated five months. The setbacks—which included issues with data submission by component bodies, incomplete and inaccurate report outputs, and various performance issues—took the Treasury significantly longer than would be expected to understand and resolve. The Treasury’s failure to identify and resolve these issues before the system was live indicates insufficient user acceptance testing and weaknesses in the system specification. The Treasury reports that all known issues have now been resolved ahead of the production of the 2020–21 WGA, but it anticipates that new issues may yet arise. The Treasury must demonstrate that it is now positioned to successfully manage any new issues in the normal course of business, without again impacting the overall timetable for accounts production. Recommendation: The Treasury should undertake a lessons-learnt exercise, specifically addressing but not limited to the root causes of poor design specification and testing of OSCAR II, and ensure identified improvements are implemented when applying future system changes. 6 Whole of Government Accounts 2019–20