A proposal by the Financial Reporting Council (FRC) to issue a UK version of the International Standard on Sustainability Assurance (ISSA) for use on a voluntary basis by UK assurance providers is being consulted on by the regulator.

The FRC says proposed alignment with ISSA 5000 will minimise burdens for firms carrying out assurance engagements across multiple jurisdictions and contribute to greater international alignment of sustainability assurance engagements. 

Having a UK version will also promote its use among UK assurance practitioners, leading to consistent, quality sustainability assurance engagements across the UK market, the regulator says.

The FRC is proposing only one modification to ISSA 5000 for the UK market: ISSA (UK) 5000 will include a safeguard that prohibits the use of direct assistance by internal auditors in sustainability assurance engagements. This is consistent with an existing prohibition for audits of financial statements in the UK.

There are no plans to revise the UK Ethical Standard to bring sustainability assurance into scope. The FRC says it will continue to monitor whether this is appropriate.

The profession-agnostic assurance standard supports application by both professional accountants and other assurance practitioners, provided they meet the relevant quality management and ethical requirements. 

The FRC is proposing an effective date for assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026, or as at a specific date on or after 15 December 2026.

Mark Babington, the FRC’s Executive Director of Regulatory Standards, said: “As sustainability assurance matures, it is important that the UK establishes a consistent sustainability assurance framework that underpins investor confidence in UK sustainability reporting. The proposed adoption of this standard demonstrates the FRC’s continued commitment to internationally consistent audit and assurance frameworks, while allowing flexibility through voluntary use.

During its recent study of the UK sustainability assurance market, stakeholders including ICAEW expressed support for an assurance framework that provides a clear and internationally consistent approach to sustainability assurance.

ICAEW’s submission to the sustainability assurance market study, published in November last year, called for alignment with international reporting and assurance standards, saying that a decision on the UK adoption of ISSB reporting standards would provide much needed direction to the UK. 

Nigel Sleigh- Johnson, ICAEW Director of Audit and Corporate Reporting, commented: “We strongly support alignment with international reporting and assurance standards, and are strongly supportive of ISSA 5000. We are pleased to see the proposals for UK adoption include minimal amendments, supporting the drive for a widely applied, internationally recognised assurance standard, avoiding unnecessary fragmentation.”

The FRC says it does not believe that a UK version of ISSA 5000 will result in additional costs for business given the voluntary nature of the standard. “Assurance practitioners can already use the international version of the standard, and there should be no additional costs to use the UK version as we are not proposing any additional requirements,” it says.

The FRC is encouraging all interested parties – including assurance providers, investors, businesses and sustainability experts – to respond to the consultation, which it says will help shape the future of sustainability reporting in the UK. The consultation is open until 31 July 2025. To participate, email AAT@frc.org.uk.

More information 

Read the consultation

Read the summary of findings from the FRC’s market study on the UK’s sustainability assurance market

Read the IAASB’s ISSA 5000 Implementation Guide providing practical non-authoritative guidance intended to assist practitioners in implementing ISSA 5000