Summary
The 2026 Green Book is more than 40 per cent shorter than its predecessor, but a more judgement-led framework raises the bar rather than lowering it. The cases that hold up under scrutiny share a small number of disciplines, but, more usefully, they keep earning their keep long after the funding decision, serving as a clear and agreed statement of what a scheme is for, as well as what a project will deliver and how. Treating appraisal as a submission rather than an operating document is one of the more expensive habits in the sector.
A shorter Green Book, not an easier one
The revised Green Book was published on 5 February 2026, and at under a hundred pages, it was more than 40 per cent shorter than its predecessor. Evaluation has been separated out altogether, directing practitioners to the newly elevated Magenta Book for what follows, and process guidance on developing business cases now sits in its own suite of online documents, templates and guidance, refreshed in June 2026.
Three points matter for capital, infrastructure and regeneration bids. The Treasury does not endorse arbitrary benefit-cost ratio thresholds. The Treasury makes it even clearer that value for money is a rounded judgement across monetised and un-monetised impacts, not a single number above a line. That had always been the case, but form, habit and schemes from individual government departments had created a monster.
Attention has been rebalanced across the Five Case Model, so that the economic case does not distort scope to the point where a scheme becomes undeliverable. A strong Benefit-Cost Ratio (BCR) with a weak management case is not a strong business case. And the emphasis has moved from procedure towards judgement. That is welcome, but it raises the bar. Where guidance had previously prescribed, a practitioner could simply comply; where it calls for judgement, a practitioner must be able to support the case with strong evidence. In this regard, the Green Book has followed where Subsidy Control led – gone is the box-ticking; now the content must be completely thought through.
Why do sound schemes still come unstuck?
Anyone who has sat on the wrong side of a funding decision will recognise the pattern. The scheme is sound, the need is obvious, and the bid returns with a short note about the counterfactual, or a polite observation that the benefits appear to have been assumed rather than evidenced. It is rarely the ambition that fails. It is the reasoning. Across the cases we prepare and independently review for local authorities, combined authorities and development companies, the same weaknesses recur:
- A counterfactual asserted rather than constructed. “Nothing happens” is almost never true, and almost always challenged.
- Additionality treated as a percentage rather than an argument, with standard ratios standing in for local market evidence.
- Optimism bias applied as a token uplift at the foot of a cost line, unreconciled with the risk register in the management case.
- Un-monetisable benefits — health, town centre confidence, safety — relegated to flowery prose rather than assessed.
- Sensitivity analysis that is decorative: presented, but incapable of telling a decision-maker anything they could act on.
None of these is especially difficult to put right. Nearly all of them are difficult to put right late in the day.
What is a business case worth after the decision?
This is the part that attracts least attention and repays the most. Approval is not the end of an appraisal’s working life; it is the start of a five- to ten-year period in which the business case is the only document recording, in one place, what the scheme is for, what it should deliver, at what cost and on what assumptions. That matters in four situations which arrive in almost every programme.
When costs move. A case with properly worked switching values already knows how far build cost, occupancy or capture rate can shift before value for money turns — so the team can answer the question that matters: which elements of scope preserve the benefits, without commissioning a fresh appraisal under time pressure.
When scope has to change. Together, the counterfactual and the theory of change form the test for change control. If a variation weakens a causal link the funder had believed, that shows up immediately and highlights the need to rethink an entire project; if it does not, the change can be approved quickly and defensibly.
When benefits must be evidenced. With evaluation now hitched firmly to the Magenta Book, the appraisal’s baseline, indicators and distributional analysis become the monitoring framework by default. Cases written with that second life in mind produce attributable outcomes; cases written only to pass produce a reporting problem in year three.
When the team changes. A traceable case — every material assumption with a stated source and rationale is the institutional memory that survives officer turnover.
| Before the decision | After the decision | |
| Counterfactual | Justifies intervention | Test for change control |
| Switching values | Demonstrates confidence | Early warning on viability |
| Benefits and indicators | Support the VfM judgement | Monitoring and evaluation baseline |
| Optimism bias and risk | Adjusts the appraisal | Reconciles to the delivery risk register |
Where the trade-off bites
There is a cost to building a case purely to clear a threshold. An optimism bias adjustment reverse-engineered to protect a target BCR does more damage than a larger, honest one — not only at assurance, but eighteen months in, when costs have moved and nobody can say which benefits remain intact. Realistic optimism is cheaper than a mid-programme reset.
Two developments worth reflecting now
Place-based business cases. Early adopter work is under way in Liverpool, Birmingham, Plymouth and Port Talbot, testing how appraisal can assess a coordinated package of interventions in a place rather than schemes assessed in isolation. Guidance is expected to follow, but the direction of travel is clear enough to reflect now in any prospectus spanning interdependent projects: shared objectives, a single theory of change for the place, and an honest treatment of the interactions between schemes.
The discount rate. The independent review led by Professors Freeman and Groom reported in June 2026, recommending a cut in the headline rate from 3.5 to 3.0 per cent on the basis that the current rate may undervalue long-term transformational benefits. The Treasury has yet to confirm its response, so 3.5 per cent remains operative. Schemes with long benefit profiles are well advised to test both: a case that already knows how it performs under a revised rate will not need rewriting later.
Conclusion
The reforms of the past eighteen months have made the Green Book easier to read. They have not made it easier to satisfy, and a more judgement-led framework rewards those who can reason carefully and penalises those who rely on it to do the reasoning for them.
The encouraging part is that a well-constructed case is usually shorter than a poorly constructed one — and that the effort is recovered several times over during delivery, rather than spent at the point of submission.
Mickledore prepares and reviews Business Cases for clients across the UK, covering strategic outline, outline and full business cases for capital, infrastructure and regeneration investment. We also deliver Green Book training for in-house teams. If you would like to discuss an appraisal in preparation, or would value an independent review before submission, we would be pleased to hear from you at nwilcock@regionaldevelopment.co.uk