PAS 91 vs Common Assessment Standard (CAS): choose compliance without compromise.
Summary
In this guide you’ll learn:
- What PAS 91 and the Common Assessment Standard (CAS) are—and how they differ.
- When each standard is typically required in UK construction procurement.
- Why many buyers run both—and how to minimise duplication.
- How Samson (PAS 91 & CAS compliant) streamlines supplier pre‑qualification.

If you buy or supply services in the UK construction sector, you’ve almost certainly heard of PAS 91. In recent years the Common Assessment Standard (CAS)—championed by Build UK—has risen as a newer benchmark. With two frameworks in circulation, procurement teams often ask: Do I need both? Which one is mandatory? How different are the questions? This guide answers those questions and shows why a digital platform like Samson—compliant with PAS 91 and CAS—makes managing supplier pre‑qualification a breeze.
What Is PAS 91?
- Developed by the British Standards Institute (BSI).
- Standardises the Pre‑Qualification Questionnaire (PQQ) for construction.
- Widely used by public authorities and private contractors.
- Focuses on core business, H&S, environmental, and financial checks.
PAS 91 remains the default requirement in many public‑sector tenders.
What Is the Common Assessment Standard (CAS)?
- Created by Build UK in collaboration with CECA and industry partners.
- Aims to rationalise multiple pre‑qualification schemes (e.g., CHAS, Constructionline, Achilles).
- Includes question modules aligned to PAS 91 plus additional checks on modern slavery, sustainability, and diversity.
- Delivered via approved assessment bodies at two levels:
- Desktop (Level 1)
- Site‑based (Level 2)
CAS is increasingly specified by Tier 1 contractors looking to reduce duplication across their supply chains.
Side‑by‑Side Comparison
Feature / Module | PAS 91 | Common Assessment Standard (CAS) |
---|---|---|
Governing body | BSI | Build UK |
Core business information | ✔️ | ✔️ |
Financial standing | ✔️ | ✔️ |
Health & Safety | ✔️ | ✔️ (expanded) |
Environmental management | ✔️ | ✔️ |
Equal opportunities & diversity | ✔️ | ✔️ (detailed) |
Modern slavery | ✖️ | ✔️ |
BIM capability | Optional | Optional |
Assessment levels | Single | Level 1 (desktop), Level 2 (site) |
Recognition by public sector | High | Growing |
CAS and PAS‑91 share ~70% of their contents. |
Which Standard Should You Use?
Scenario | Recommended Standard |
---|---|
Public‑sector project (local authority, NHS, MoD) | PAS 91 (mandatory in many frameworks) |
Private Tier 1 contractor aligned with Build UK | CAS (often preferred) |
Mixed supply chain or long‑term framework | Both (ensure suppliers can satisfy either requirement) |
The safest route is to collect data that satisfies both standards—especially when subcontractors may work across multiple clients.
How Samson Keeps You Compliant with PAS 91 and CAS
- Dual templates: Out‑of‑the‑box questionnaires for PAS 91 and CAS.
- Customisable Questionnaires: The questionnaires can be full customised to meet your unique requirements.
- Expiry tracking: Alerts when insurances or certificates lapse.
- Audit trail: Review past questionnaires.
Transitioning From PAS 91 to CAS: 4‑Step Plan
- Gap analysis – Identify CAS questions not covered by your current PAS 91 form.
- Supplier comms – Notify suppliers of the upcoming change and provide guidance.
- Dual period – Accept both standards during a defined transition window.
- Fully adopt CAS – Once ≥80% of suppliers meet CAS, switch primary requirement.
Samson’s flexible workflows let you run both standards in parallel until your supply chain is ready.
Frequently Asked Questions
Is CAS legally required?
No, but many Build UK members now specify it to streamline their supply chains.
Will PAS 91 be phased out?
Not yet. Government frameworks still rely on PAS 91, but CAS adoption is growing.
Can suppliers certified to CAS skip PAS 91?
Often yes, because CAS Level 1 covers PAS 91 core questions. Always confirm with the buyer.
Does Samson support both PAS 91 and CAS forms?
Absolutely—Samson ships with up‑to‑date templates for each, plus automatic version control.
Conclusion: Choose Compliance Without Compromise
Both PAS 91 and the Common Assessment Standard aim to make pre‑qualification simpler and safer—but juggling two frameworks can create new admin headaches. Digital platforms like Samson solve this by unifying data capture, automating compliance checks, and giving buyers a single source of truth.