Transparency data

Accounting Officer Assessment: NS&I’s Business Transformation (formerly Rainbow) Programme 2026

Updated 4 November 2026

31 July 2026

It is normal practice for Accounting Officers to scrutinise significant policy proposals or major programmes and assess whether they measure up to the standards set out in HM Treasury’s Managing Public Money guidelines. This assessment has been undertaken in support of the revised Programme Business Case for NS&I’s Business Transformation Programme following consideration of alternative delivery approaches.

Background and context

The NS&I Business Transformation (formerly Rainbow) Programme (the ‘BTP’) was launched in 2020 to modernise NS&I’s operating model, which included moving NS&I from a single-supplier outsourced model to a multi-supplier model for greater resilience and updating NS&I’s ageing systems to make it a more cost-effective, scalable and agile source of government finance.

As delivery progressed, it became apparent that the original delivery assumptions underestimated the complexity of replacing a highly integrated legacy technology and data estate, the capability required to manage delivery across multiple suppliers, the commercial and technical dependencies involved, and the time and cost required to deliver the intended outcomes. As a result, the BTP has experienced significant delays and cost increases. The plan approved in the December 2024 Full Business Case by the then Chief Secretary to the Treasury and Economic Secretary to the Treasury is no longer considered viable.

NS&I and HM Treasury have subsequently assessed alternative delivery approaches and NS&I has developed a revised Programme Business Case (PBC). Having considered the evidence presented, I support the recommended alternative approach (the ‘Simplified Solution’) and the revised Programme Business Case. The preferred option is expected to deliver the intended strategic outcomes of the BTP and provide the best balance of value for money and deliverability when compared with the alternative options considered.

The preferred option exceeds the 2025 Spending Review allocation with affordability implications being considered by HM Treasury as part of the PBC approval process.

Assessment against the Accounting Officer standards

This Accounting Officer Assessment has been undertaken by me, Sir Jim Harra, NS&I Accounting Officer and Interim Chief Executive. In reaching my assessment, I have considered the evidence presented within the revised Programme Business Case, the recommendations of the Senior Responsible Owner for the BTP and advice from the People & Finance Director. I am satisfied that the development of the revised Programme Business Case has been informed by appropriate commercial, financial and programme advice, and that relevant specialist analysis and assurance has been considered as part of its preparation.

I have also considered the views and challenge provided through the programme’s governance arrangements, including the Programme Board, Executive Committee and Board Transformation Sub-Committee, which is chaired by a Non-Executive Director and provides independent challenge and oversight of the BTP.

This assessment reflects the material changes to the programme following the review of delivery options and the proposed programme reset. It considers the evidence supporting the recommended approach and the extent to which it addresses the findings and recommendations arising from recent internal and external assurance activity.

The assessment considers the four Accounting Officer standards set out in Managing Public Money: regularity, propriety, value for money and feasibility.

Regularity

NS&I is both a non-ministerial government department and an Executive Agency of the Chancellor of the Exchequer. It is responsible for raising cost-effective financing for government through retail savings and investment products, providing administration services to other government departments through NS&I Government Payment Services, and supporting the delivery of government policy. The National Debt Act 1972 and National Savings Bank Act 1971 detail the existence of NS&I and set out my authority, as Director of Savings, for carrying out the business of NS&I.

The BTP covers transformation of NS&I’s operating model, including the re-procurement of NS&I’s outsourced business process service delivery, new technology and enhanced internal capabilities to enable NS&I to manage a multi-supplier model.

Expenditure relating to the BTP falls within the ambit of NS&I’s Estimate. This includes expenditure required to deliver and transform NS&I’s operations, including technology replacement, operating model transformation, programme delivery activities, capital investment and associated non-cash accounting adjustments.

I have considered the evidence presented within the revised Programme Business Case, including the implications of the proposed commercial reset and the approvals required to implement the recommended option, and am satisfied that these have been informed by appropriate specialist analysis, advice and assurance.

[Redacted]  Implementation of the preferred option may give rise to [redacted] matters exceeding the Accounting Officer’s delegated authority [which] will be subject to the appropriate HM Treasury approval process following approval of the revised Programme Business Case.

Summary: Based on the evidence presented within the revised Programme Business Case, I am satisfied that the BTP is supported by the necessary legal powers and falls within the ambit of NS&I’s Estimate. Implementation of the preferred option will be subject to the necessary HM Treasury, governance and delegated authority approvals being secured. The commercial reset may give rise to provisions, liabilities and other accounting implications which are continuing to be assessed. Any matters exceeding the Accounting Officer’s delegated authority will be subject to the appropriate HM Treasury approvals process. Subject to these approvals being secured, I am satisfied that no issues of regularity arise.

Propriety

The BTP is compliant with parliamentary control procedures and expectations. The programme forms part of the Government Major Projects Portfolio (GMPP) and will continue to engage with the National Infrastructure and Service Transformation Authority (NISTA), Government Commercial Agency and Cabinet Office Commercial Standards and Assurance Team to ensure it continues to reflect recognised government best practice.

NS&I has developed the revised Programme Business Case in accordance with relevant legislation, regulations and guidance, including the Public Contracts Regulations 2015, Government Legal Services Model Services Contract, Government Digital Service Technology Code of Practice, Government Commercial Agency Balanced Scorecard and the Government Commercial Function Outsourcing Playbook. The revised Programme Business Case has also been informed by the findings and recommendations from the National Audit Office study (November 2025), Public Accounts Committee hearing report (February 2026), David Goldstone CBE’s independent review (April 2026) and NISTA review (June 2026). These reviews highlighted the need for a more credible integrated plan, stronger delivery controls, clearer accountability, improved risk management, and more robust cost and benefits evidence. I have considered how these findings have informed the revised programme approach and governance arrangements set out within the revised Programme Business Case.

Summary: Based on the evidence presented within the revised Programme Business Case and recognising that its development has been informed by appropriate commercial, financial and programme advice, I am satisfied that the programme is being undertaken in accordance with relevant government standards, guidance and parliamentary expectations, and that no issues of propriety arise.

Value for Money

In line with HM Treasury Green Book principles, a proportionate appraisal of the available delivery options, including a minimum investment option, has been undertaken and is set out in the revised Programme Business Case. The appraisal reflected the material change in BTP’s circumstances since the 2024 Full Business Case, including affordability pressures, delivery confidence, legacy technology risk and the complexity of the target operating model.

It is essential that NS&I remains operational when several critical technology components are expected to move beyond extended support over the next two to three years. Failure to replace the core banking capability would expose NS&I to increasing operational, resilience and service risks. Having considered the analysis contained within the revised Programme Business Case, I am satisfied that the preferred option provides the best overall balance of value for money and deliverability when compared with the alternative options considered, including doing the minimum necessary to maintain operations.

Summary: The analysis contained within the revised Programme Business Case demonstrates that, when compared with alternative delivery options and a minimum investment approach, the preferred option provides the best overall balance of value for money and deliverability and represents the most appropriate use of public resources. Delivery remains dependent upon the necessary funding being secured.

Feasibility

[Redacted]

Since the previous Accounting Officer assessment, the National Audit Office (November 2025), Public Accounts Committee hearing report (February 2026), David Goldstone CBE (April 2026) and NISTA (June 2026) identified a number of significant delivery challenges, including weaknesses in governance, integrated planning, programme capability, management of supplier dependencies and understanding of the complexity of the legacy technology estate. The revised Programme Business Case has been developed taking account of these findings and lessons learned from programme delivery and external assurance activity to date. It incorporates a revised delivery approach, strengthened governance and controls, improved risk management, a clearer understanding of delivery dependencies, capability requirements and resource implications, and a number of changes specifically designed to address the delivery challenges identified through programme delivery and independent assurance reviews. The revised Programme Business Case is underpinned by an integrated delivery plan which provides greater clarity of dependencies, milestones, transition activities and delivery controls across the BTP.

The revised Programme Business Case demonstrates that the programme reset has considered a full and proportionate range of credible delivery options. The assessment reflects the material change in delivery context since the 2024 Full Business Case, including affordability pressures, delivery confidence, legacy technology risk, supplier and integration complexity, and the need to meet future customer and HM Treasury requirements. In particular, the recommended Simplified Solution option reduces technical integration and supplier management complexity compared with the previous BTP solution set. The revised Programme Business Case also incorporates contingency and optimism bias allowances to reflect the remaining uncertainty associated with delivery, commercial negotiations and programme implementation.

Summary: While delivery of a programme of this scale remains challenging, the revised delivery approach, strengthened governance arrangements, recovery actions and planned commercial negotiations provide a credible and achievable route to delivering the BTP and its intended outcomes. This remains subject to the necessary funding being agreed, including the financial support and approvals required to enable delivery of the BTP across the SR25 period.

Conclusion

Having considered the evidence presented within the revised Programme Business Case and recognising that its development has been informed by appropriate commercial, financial and programme advice, I am satisfied that the proposed approach meets the standards of regularity, propriety, value for money and feasibility set out in Managing Public Money, subject to the necessary funding and approvals being secured to enable delivery of the programme.

In reaching this conclusion, I have taken account of the significant delivery challenges experienced by the BTP to date and the actions taken to strengthen governance, capabilities, planning and delivery confidence.

As the Accounting Officer for NS&I, I assessed the Business Transformation Programme and approved it on 31 July 2026.

I have prepared this summary to set out the key points which informed my decision. If any of these factors change materially during the lifetime of this programme, I will prepare a revised summary setting out my assessment of them.

This summary will be published on the Government’s website (GOV.UK). Copies will be deposited in the Library of the House of Commons and sent to the Comptroller and Auditor General and the Treasury Officer of Accounts.

Sir Jim Harra NS&I Accounting Officer and Interim Chief Executive

This summary reflects the Accounting Officer Assessment undertaken on 31 July 2026. Since completion of that assessment, ministerial approval of the revised Programme Business Case was received on 5 October 2026. This update is included to provide readers with the current status of the Programme. The Accounting Officer Assessment set out above remains the assessment undertaken and concluded on 31 July 2026.