CEST, SDS and contract review: who decides what
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Three assessments, three owners, three levels of reliability. Contractors mix them up constantly — here's the map.
| Assessment | Owner | Binding on HMRC? | Use it for |
|---|---|---|---|
| CEST (HMRC tool) | Whoever runs it | No — but HMRC stands by its results where inputs are accurate | A quick first read; weak on substitution and MOO |
| SDS | Medium/large end client | Creates the client-led liability chain | The operative determination for your engagement |
| Specialist contract review | Your adviser | Nothing — but spots the clauses that lose cases | Pre-signature risk control and insurance underwriting |
How to use them together
Run CEST yourself as a smoke test, demand the SDS as the operative document, and get the contract reviewed before signature. If CEST says outside but the SDS says inside on identical facts, the SDS reasons (or the facts behind them) are wrong — challenge in writing, with 45-day response rights. Insurance underwriters will want all three anyway before covering status risk.
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