The OTR GroupIf you have worked on a public-sector project, you will have met the Five Case Model. It is the structure used in the Green Book, HM Treasury''s guidance on appraisal and evaluation, to build a business case. Even outside government, it is a useful checklist for anyone asking whether an idea is worth doing. This guide sets out the five cases in plain English, using the wording of the 2026 edition of the Green Book.
The strategic case
The Green Book says this sets out the rationale and objectives for the intervention. It covers the case for change, a theory of change, SMART objectives, business as usual and strategic fit. In everyday terms: why are we doing this, and what do we want to achieve?
The economic case
This sets out the longlist and shortlist of options for achieving the objectives, and identifies the preferred option that delivers the best value for money. Critical success factors sit here, along with the longlist and shortlist appraisal. The plain-English question: of the ways we could do this, which gives the best value?
The commercial case
The Green Book describes this as how government will source the inputs required to deliver the preferred option, and who will manage the risks associated with delivery and operation. It covers procurement strategy, service requirements, risk allocation, charging mechanism, key contractual arrangements and personnel implications. Put simply: can we buy what we need, and who carries which risk?
The financial case
This is concerned with the affordability of the proposal for the public bodies involved. It looks at public sector costs, the impact on income, expenditure and balance sheet, and overall affordability and funding. The question: can we pay for it?
The management case
This sets out the practical arrangements for implementation and demonstrates that the preferred option can be delivered successfully. It covers governance, change management, benefits realisation and risk management, a monitoring and evaluation plan, and contingency arrangements. The question: can we actually deliver it?
How the stages fit together
The Green Book describes three stages of developing a project business case. The Strategic Outline Case is the first stage: it makes the case for change, identifies SMART objectives and sets out an initial longlist and shortlist of options. The Outline Business Case is the second stage: it revisits the options to identify the preferred option following more detailed analysis, and outlines commercial, financial and management arrangements. The Full Business Case is the third stage: it sets out the full details of the commercial, financial and management arrangements required to deliver the project, following the procurement process.
A quick self-check
- Can you state the objective in one sentence?
- Have you compared more than one way of achieving it?
- Do you know how you will buy or build what is needed?
- Is the cost affordable for the organisation paying?
- Is there a named owner and a plan for delivery and review?
If any answer is unclear, that is the case to strengthen first.
Where to read more
The Green Book was last updated on 28 October 2026, and the separate business case guidance for projects and programmes is published on GOV.UK. For any formal submission, rely on the current official text rather than a summary like this one.
Source: HM Treasury, The Green Book 2026, GOV.UK.