Purpose: How to evolve an SCM from early option appraisal into a more detailed tool for market engagement, affordability and supplier-proposal analysis.
How to evolve an SCM from early option appraisal into a more detailed tool for market engagement, affordability and supplier-proposal analysis. This matters because public procurement decisions are rarely isolated events. A choice made during planning can affect competition, affordability, service quality, supplier behaviour and the ability to manage the contract later. The strongest approach is therefore to use the source guidance as part of an end-to-end commercial process, with clear ownership and evidence rather than as a document that is completed after the key decisions have already been taken.
Quick summary
- The guidance presents the SCM as an evolving model, not a one-off estimate.
- Early SCMs can support Delivery Model Assessment and make-versus-buy decisions.
- An expected market cost view can inform market engagement and the commercial strategy.
- The model can become more detailed as requirements, volumes and evidence improve.
- The SCM can help analyse movements between expected cost and supplier proposals.
What the guidance means in practice
The source material gives several anchors for that process. The guidance presents the SCM as an evolving model, not a one-off estimate. Early SCMs can support Delivery Model Assessment and make-versus-buy decisions. An expected market cost view can inform market engagement and the commercial strategy. These are not interchangeable statements: some describe statutory or policy requirements and others describe recommended commercial practice. Teams should identify which category each requirement falls into, apply it to the organisation and procurement in scope, and keep a record of the judgement. Where guidance from 2021 or 2023 predates the Procurement Act 2023, its commercial principles can remain useful, but current legislation, regulations and current statutory guidance take precedence on legal process.
The practical value becomes clearer when the remaining guidance is read alongside the project lifecycle. The model can become more detailed as requirements, volumes and evidence improve. The SCM can help analyse movements between expected cost and supplier proposals. The development lifecycle includes planning, model design, development, testing, quality assurance and controlled use. In day-to-day terms, this means the buyer should be able to answer three questions at any approval point: what outcome are we trying to achieve, what evidence supports the proposed commercial approach, and what will need to be managed after the decision is made? If those answers are weak, more analysis is normally more useful than adding another layer of narrative to an approval paper.
A practical process to follow
A proportionate process can be built into existing governance. The steps below are deliberately practical. They are not a substitute for the detailed source guidance, legal advice or local standing orders, but they provide a useful structure for a procurement or commercial team.
- Step 1. Create a simple strategic model early enough to influence delivery options. Record any assumption that could change the conclusion and when it will be reviewed.
- Step 2. Use market engagement to test cost structure, drivers and assumptions. Keep the analysis proportionate to the value, risk, novelty and criticality of the requirement.
- Step 3. Increase model detail only when the decision requires it. Capture the source evidence and name the person accountable for the next decision.
- Step 4. Freeze and quality-assure a version for key approval or procurement use. Record any assumption that could change the conclusion and when it will be reviewed.
- Step 5. Reconcile supplier proposals to the model so scope and assumption differences are visible. Keep the analysis proportionate to the value, risk, novelty and criticality of the requirement.
- Step 6. Retain relevant cost drivers for contract management and future re-procurement. Capture the source evidence and name the person accountable for the next decision.
What good looks like
Good practice is visible in the decision trail, not only in the final document. A reviewer should be able to follow the line from the service need, through market and cost evidence, to the route, evaluation, contract terms and management arrangements. Where several functions contribute, the file should show who owns each decision and where challenge occurred. The same principle applies to handover: useful assumptions, models, KPI definitions, risks, supplier information and approval conditions should move into mobilisation and contract management instead of being left in the sourcing archive. This continuity is particularly important for long-running public services, where staff can change but the organisation remains accountable for the outcome.
Recommendations for procurement teams
The following recommendations are suitable for teams that want to embed the topic into normal ways of working rather than create a parallel compliance process:
- Set version-control rules from the first model.
- Record why assumptions change between stages.
- Align the model with specification, volumes and pricing schedules.
- Avoid changing evaluation-relevant assumptions after bids arrive unless the procurement process lawfully permits it.
- Use sensitivity analysis to show decision makers what matters most.
- Capture actual delivery data to improve the next model.
Common pitfalls to avoid
The most common problems are usually process failures rather than a lack of templates. Watch particularly for the following:
- Letting the model become detached from the service design.
- Adding complexity without improving the decision.
- Changing cost categories so earlier comparisons become impossible.
- Discarding the model after contract award.
Easy-to-read takeaway
For how a should cost model should evolve through the procurement lifecycle, the core discipline is to start early, connect the analysis to a real decision and preserve enough evidence for the next stage of the lifecycle. The source material should help teams make better decisions, not merely produce more paperwork. Before acting on a live procurement, confirm the current version of the Procurement Act 2023, regulations, Procurement Policy Notes and any organisation-specific approvals or delegations. This is especially important for thresholds, notice duties, exemptions and policy requirements that can change over time.
Source basis
Primary source used: Should Cost Modelling Guidance Note, May 2021. Related articles in this collection also draw on the other supplied Cabinet Office, HM Treasury and Procurement Act materials where the topics overlap.
This article is general procurement support content. It should be read alongside current legislation, statutory guidance and your organisation’s own governance and legal advice.