Looking forward to ISSA (UK) 5000
Mark Lumsdon-Taylor · Posted on: December 23rd 2025 · read
On 12 November 2025 the Financial Reporting Council announced the publication of ISSA (UK) 5000, titled General Requirements for Sustainability Assurance Engagements.
ISSA 5000 established by the International Auditing and Assurance Standards Board (IAASB), setting a global standard for verifying sustainability information. It covers requirements for assurance engagements on sustainability information, from acceptance to reporting.
The standard exists to provide a consistent and unified approach to sustainability reporting, addressing the need for trustworthy sustainability information and enabling the proper assessment and communication of ESG (Environmental, Social, Governance) information.
The ISSA 5000, General Requirements for Sustainability Assurance Engagements and Conforming and Consequential Amendments to Other IAASB Standards Arising from ISSA 5000, has been published by the IAASB, with ISSA 5000 being effective for assurance engagements on sustainability information reported for periods beginning on or after 15th December 2026.
According to Tom Seidenstein, Chair of the IAASB, ‘we are at the advent of a new era of external reporting. Users will expect a broader range of information – financial and non-financial information – to assess corporate performance’.
The principles-based stand-alone ISSA 5000:
- Is suitable for any sustainability assurance engagement
- Can be applied to sustainability information reported across any sustainability topic and prepared under multiple frameworks
- Supports the application of traditional financial materiality and double-materiality that unites financial materiality and impact materiality
- Deals with reasonable and limited assurance engagements and differences in associated work efforts
- Supports use by professional accountant and non-accountant practitioners
- Includes guidance on application and other explanatory material
And the UK
The ISSA (UK) 5000 consultation process was published on 29 May 2025, closing on 31 July 2025.
It resulted in the FRC issuing a UK version of IAASB’s ISSA 5000 for use on a voluntary basis by UK assurance providers. While voluntary now, the FRC has signalled that ISSA (UK) 5000 is expected to become part of the UK’s future sustainability assurance framework.
The ISSA (UK) 5000 applies to all assurance engagements on sustainability information, regardless of how that information is presented. It addresses both reasonable and limited assurance engagements, including attestation engagements.
A practitioner will not be required to apply ISAE (UK) 3000 when performing an engagement under ISSA (UK) 5000.
Objectives of the UK standard
In conducting a sustainability assurance engagement, the objectives of the practitioner are:
- To obtain reasonable assurance or limited assurance about whether the sustainability information is free from material misstatement
- To express a conclusion on the sustainability information through a written report that conveys a reasonable assurance or a limited assurance conclusion, as well as describing the basis for that conclusion
- To communicate further as required by this and any other relevant ISSA (UK)
Where assurance cannot be obtained and a qualified conclusion is insufficient, the practitioner must disclaim a conclusion or withdraw from the engagement (where permitted by law or regulation).
In exceptional circumstances, departures from a requirement must be documented, with alternative procedures performed to achieve the aim of that requirement.
The full details of the proposed ISSA (UK) 5000 may be found on the Financial Reporting Council website at: https://media.frc.org.uk/documents/Proposed_ISSA_UK_5000.pdf
Audited financial statements
ISSA (UK) does not address sustainability information included in financial statements under the applicable reporting framework. The auditor of financial statements must apply International Standards on Auditing.
Sustainability information may appear alongside audited financial statements (e.g., in an annual report) or in separate documents. Audited financial statements are considered “other information” for ISSA (UK) purposes.
Entities in scope
Bearing in mind ISSA (UK) 5000 is intended for voluntary use on assurance engagements relating to sustainability information for all entities, regardless of size or complexity.
Our expert's final thoughts
"ISSA 5000 has been well received by audit bodies and practitioners and brings a new level of transparency and consistency to sustainability reporting.
With investors and stakeholders increasingly demanding high quality, comparable and consistent disclosure standards, ISSA 5000 has a vital role to play."
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