The verdict in three sentences
A precise requirements spec is the life insurance of your custom software project: it turns a fuzzy budget into a quantifiable commitment. In 2026, in London, a formal scoping phase of GBP 3,000 to 10,000 cuts change orders by 25 to 50 % on a GBP 50,000-150,000 project. The golden rule: never sign a fixed commitment without a scoping lot or a prior POC.
What the spec must contain
A vague document produces vague quotes, hence overruns. Structure it around seven essential blocks, each contrasting good and bad practice.
| Spec block | Common mistake | 2026 best practice |
|---|---|---|
| Target processes | "Manage orders" | Flow diagram, actors, exceptions |
| User stories | Feature list | "As an X, I want Y so that Z" |
| Acceptance criteria | Absent | Testable Given/When/Then |
| Integrations | "ERP compatible" | API, format, frequency, volume |
| Volume | Unquantified | 500 users, 10,000 orders/day |
| GDPR | One line | Register, retention, DPO, processing |
| Reversibility | Forgotten | Standard export + code ownership |
Every acceptance criterion written upstream removes a contractual dispute downstream.
The cost of scoping and its return
Paying for scoping before committing looks like an extra cost; it is in fact the best risk-reduction ratio of the project.
| Item | 2026 ballpark (GBP) | Effect on the project |
|---|---|---|
| Scoping workshop (2-3 days) | 3,000 - 6,000 | Scope locked |
| Written spec + user stories | 4,000 - 10,000 | Comparable vendor quotes |
| Paid POC (1 key process) | 5,000 - 15,000 | Feasibility proven |
| Change orders avoided (GBP 100k project) | -12,000 to -35,000 | Direct scoping ROI |
| Go-live delay avoided | 1 to 3 months | Reduced opportunity cost |
On a GBP 100,000 project, avoiding two 8 % change orders repays the scoping several times over.
Legal clauses never to forget
Three clauses protect the CIO long term: source code IP ownership (delivery to a repository you own), reversibility (data export in a documented standard format) and application maintenance (framed TMA with SLA and a capped hourly rate). Without them, a vendor can lock you in and turn your software into technical debt.
Mini case study
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Mark, CIO of a B2B distribution SME in London (180 staff), launches an RFP for a sales management system. He hesitates to pay GBP 8,000 for scoping. On his estimated GBP 110,000 project, company history showed 3 average change orders of GBP 9,000 per poorly scoped project, i.e. GBP 27,000. By investing the GBP 8,000, Mark cuts change orders to just one (GBP 9,000): a net saving of GBP 10,000 and a go-live brought forward by 6 weeks. Scoping paid back 2.25 times its cost.
FAQ
How long does it take to write a good requirements spec?
Allow 2 to 5 weeks depending on complexity, including several business workshops. A rushed one-week spec costs more in change orders than it saves in time.
Do you need a spec if you pick off-the-shelf software rather than custom?
Yes, but a lighter one: it serves as an evaluation grid to compare vendors. Even trimmed, it makes the selection objective and avoids buying on a slick demo.
Who should write the spec?
Ideally a pairing of business staff plus a neutral scoping provider. Handing the spec to the chosen vendor creates a conflict of interest: they will write what their product does.
How do you avoid budget overruns?
Testable acceptance criteria, quantified volume and a paid POC on the riskiest process. These three cover 80 % of overrun causes in 2026.
What exactly does the reversibility clause cover?
Export of your data in a documented standard format, access to source code and transferability to another provider. It protects you if the vendor relationship sours.
Let's scope your project. Describe your target processes, your volumes and your indicative budget, and we will scope an RFP-ready spec together. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
