Sustainability assurance in the UK: what is required, and which standard

No. No UK law or regulation requires a company to obtain assurance over its sustainability disclosures. The FCA's final UK SRS rules require listed companies to say whether they obtained assurance, not to obtain it, and the government's September 2026 consultation says it has no plans to introduce assurance requirements for UK SRS reporting at this stage. Verification of emissions reports under UK ETS is mandatory, but that is a different regime.

Under UKLR 6.6.6R(8)(d), for accounting periods beginning on or after 1 January 2027, a listed company states whether or not it has obtained third-party assurance over its UK SRS disclosures. If it has, it names the provider, says which disclosures were assured and to what level, names the assurance standards used, and says where any published assurance report can be found. The FCA does not require an explanation where assurance was not sought.

ISSA (UK) 5000, General Requirements for Sustainability Assurance Engagements, is the UK version of the IAASB's ISSA 5000. The FRC issued it on 12 November 2025 for voluntary use. It is effective for assurance engagements on sustainability information for periods beginning on or after 15 December 2026, with earlier application permitted. It binds a practitioner who says the engagement complied with it; it compels no company to obtain assurance.

ISAE 3000 (Revised) is the IAASB's general standard for assurance engagements other than audits or reviews of historical financial information, and it has been widely used for sustainability work. ISSA 5000 is a standard written for sustainability assurance. The IAASB has said ISAE 3000 will no longer apply to sustainability engagements after ISSA 5000's effective date. In the UK, ISSA (UK) 5000 says a practitioner applying it is not required to apply ISAE (UK) 3000, while the FRC still lists ISAE (UK) 3000 as a current standard.

Yes. The IAASB announced on 8 May 2025 that it had approved the withdrawal of ISAE 3410, Assurance Engagements on Greenhouse Gas Statements, and that the withdrawal takes effect from the effective date of ISSA 5000, which is for periods beginning on or after 15 December 2026.

Reasonable assurance reduces engagement risk to an acceptably low level and ends in a positive opinion that the information is prepared, in all material respects, in accordance with the criteria. Limited assurance involves procedures that are less in extent, and ends in a conclusion that nothing has come to the practitioner's attention to cause them to believe the information is materially misstated. ISSA (UK) 5000 requires a limited assurance report to say that the assurance obtained is substantially lower than in a reasonable assurance engagement.

There is no restriction in UK law. The government has decided on a voluntary oversight regime in which practitioners may opt in to a public register run by the FRC, whether or not they are auditors. The IESBA's ethics standards for sustainability assurance, effective from 15 December 2026, apply regardless of a practitioner's background. For a public interest entity client, a practitioner may not provide non-assurance services that might create a self-review threat over the information it assures.

No. The government's environmental reporting guidelines say there is no requirement in the legislation for SECR emission and energy data to be independently assured, and no statutory requirement to have environmental information audited, while recommending assurance as best practice. The guidelines date from March 2019 and name standards that are now being withdrawn, so cite them for the negative only.

The government's response of 30 January 2026 tasked the FRC with establishing an interim, non-legislative regime by mid-2026 and with having the register operational well ahead of the 1 January 2027 reporting year. On the latest record we hold, from July 2026, it had not opened. Registration is voluntary for practitioners.