What can non-audit assurance do for your business?

20 May 2026

By Liam Cheyne, AAB

In today’s business environment, trust is currency, and more than ever, stakeholders want confidence in information that goes far beyond the financial statements. That’s where non-audit assurance comes in.

Demand for non‑financial assurance and agreed‑upon procedures is growing as regulators, investors, funders, and joint venture partners expect reliable verification of ESG disclosures, internal controls, cost‑share arrangements and grant compliance. ISAE (UK) 3000 and ISRS 4400 each play a role — one giving formal assurance, the other delivering targeted factual findings — but the common benefit is independent, credible evidence that reduces risk, strengthens governance and helps organisations meet regulatory and commercial expectations.

But what’s the difference between them? And when should you use each?

What is ISAE (UK) 3000?

ISAE (UK) 3000 is the UK’s standard for assurance engagements over non‑financial information. It’s often used to provide a formal, independent opinion on whether something meets defined criteria like ESG frameworks, regulatory standards, or internal controls. It supports both:

• Reasonable assurance (high confidence, positive opinion)
• Limited assurance (moderate confidence, negative form)

Common uses include:

• ESG and sustainability assurance
• SOC 1 / SOC 2 internal controls reports
• Compliance with regulatory or voluntary frameworks
• Verifying grant claims
• Oil & gas: assurance over compliance with Standard Oil Accounting Procedures (SOAPs) when recharging costs to joint venture partners
• Cost‑share: assurance over compliance with cost‑sharing arrangements for shared infrastructure

Non-Audit assurance comparison: Reasonable Assurance vs Limited Assurance

Both reasonable and limited assurance reports are provided under ISAE (UK) 3000 (or its international equivalent ISAE 3000). Reasonable assurance provides a high level of confidence based on detailed testing and evidence‑gathering and uses a positively expressed conclusion (for example, “In our opinion…”). Limited assurance applies a narrower, risk‑based scope and lighter evidence‑gathering; its conclusion is expressed in the negative (for example, “Nothing has come to our attention…”). Limited assurance can be a cost‑effective way to give stakeholders credible, timely comfort over largely objective information, but it is not appropriate where complex judgements, significant estimates or a positive assurance opinion are required.

What is ISRS 4400?

ISRS 4400 covers agreed‑upon procedures (AUP) engagements, where the practitioner performs procedures agreed with the client and reports the factual results. AUPs do not provide an assurance opinion; they are best for targeted checks where evidence is objective and verifiable. AUP reports provide clear, independent findings for the agreed scope and are usually restricted to the users named in the engagement. AUPs can be combined with other assurance work where a broader opinion is required.

Common uses include:

• Verifying grant or donor reporting
• Testing specific transactions (e.g., payroll, procurement)
• Financial due diligence
• Compliance reviews for funders or contracts

ISAE (UK) 3000 vs ISRS 4400: A Quick Comparison

We often see organisations struggle with what level of procedures or assurance they need, especially where commercial agreements are not explicit about the required standard.

When should you consider non‑audit assurance?

• You’re publishing ESG data or sustainability reports
• You need third‑party verification for funders, regulators or other stakeholders
• You’re required to have assurance or AUPs performed on grant claims
• You want confidence in internal controls or risk management
• You’re preparing for an investment, acquisition, or new partnership
• You operate in a joint venture environment (e.g., energy or infrastructure)
• You incur costs based on cost‑share arrangements

How can AAB help?

Whether you need a full assurance opinion under ISAE (UK) 3000 or targeted procedures under ISRS 4400, non‑audit assurance can help your business build trust and meet rising expectations around governance and transparency.

At AAB, our audit services tailor each engagement to the needs of the business and the information that matters most to your stakeholders. If you’d like to understand which approach might be right for your organisation, book a short diagnostic and we’ll map the options to your risks and stakeholders. If you have any queries, or would like to discuss how we can help you with non-audit assurance, please do not hesitate to get in contact with Liam Cheyne, or your usual AAB contact.