PAS 91 vs Common Assessment Standard (CAS): choose compliance without compromise.

13 Aug 2025 • 2 min read

Summary

Compare PAS 91 and the Common Assessment Standard (CAS) for UK construction pre-qualification. Discover the key differences, when to use each, and how Samson by Liaison Systems keeps you compliant with both.

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) and Site‑based (Level 2).

CAS is increasingly specified by Tier 1 contractors looking to reduce duplication across their supply chains.

Side‑by‑Side Comparison

Which Standard Should You Use?

Scenario Table — 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.

What is PAS-91?

12 Oct 2025

PAS-91 is a standardised set of questions designed to simply the pre-qualification process.

How to effectively manage your supply chain.

15 Sep 2025

Supply Chain Management is the control of all suppliers working on a project. There are 4 main sections of Supply Chain Management: procurement, operations, distribution, and integration.

What does your pre-qualification process do about pre-construction?

12 Sep 2025

When appointing a contractor to a project, reasonable steps must be taken to ensure that the contractor has the necessary skills, knowledge and competence to complete the work and in a manner that satisfies current health & safety requirements. Pre-Construction is an important part of any project, yet this importance is overlooked by a lot of supplier databases.