UK SRS assurance is voluntary. The FCA's CP26/5 paragraph 7.5 states unambiguously:
"we are not proposing to set mandatory requirements for the assurance of sustainability reporting at this time."

There is no mandatory limited assurance requirement, no mandatory reasonable assurance requirement, and no mandatory assurance effective date in the FCA's current proposals.

What the FCA does propose is a disclosure rule — listed companies in scope of UK SRS must state in their annual financial report whether or not they have obtained third-party assurance over their UK SRS disclosures.
The assurance itself remains voluntary.

What CP26/5 actually proposes on assurance

CP26/5 chapter 7 covers assurance. The chapter has four substantive proposals:

1. No mandatory assurance. Paragraph 7.5 states the FCA is not proposing to set mandatory requirements for the assurance of sustainability reporting at this time.
   The Government is separately considering the longer-term approach to sustainability assurance market operation and oversight.

2. A disclosure rule on whether assurance has been obtained. Paragraph 7.6 proposes that listed companies in scope of UK SRS specify,
   in their annual financial report, whether or not they have obtained third-party sustainability assurance over their UK SRS disclosures. This applies to disclosures under both UK SRS S1 and UK SRS S2 (including Scope 3).
   For "explain" disclosures, any assurance undertaken over the explanation must also be disclosed.

3. Specific items to disclose where assurance is obtained. Paragraph 7.7 lists four required elements when third-party assurance has been obtained:
   

   • The name of the assurance provider
     
   • Which of the climate or sustainability-related financial disclosures have been assured, and to what level
     
   • Which assurance standards were used
     
   • Where the assurance report can be located, including a hyperlink where appropriate

4. The same disclosure rule extends to secondary listings and depositary receipts. Paragraphs 9.8 and 9.9 apply equivalent disclosure requirements to listed companies in the secondary listing and depositary receipts categories.

ISSA (UK) 5000 — the voluntary assurance standard

The FRC issued International Standard on Sustainability Assurance (UK) 5000 on 12 November 2025.
The standard is titled General Requirements for Sustainability Assurance Engagements. Key facts:

• Status: For voluntary use — it governs how an assurance engagement is performed if one is commissioned, and creates no obligation to obtain assurance
  
• Effective date: Assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026, or as at a specific date on or after that date; early application is permitted
  
• Source standard: The UK version of the IAASB's international ISSA 5000, which shares the same 15 December 2026 effective date
  
• One UK modification: ISSA (UK) 5000 prohibits direct assistance by internal auditors; that is the only change the FRC made to the international standard
  
• Scope of engagements: Both limited and reasonable assurance engagements, profession-agnostic
  
• Information in scope: All sustainability information, except sustainability information required in financial statements under the applicable financial reporting framework

ISSA (UK) 5000 covers acceptance and continuance, planning, materiality, evidence-gathering, the use of experts,
evaluating misstatements, communicating with management and those charged with governance, forming a conclusion, and reporting.

The FRC interim register of sustainability assurance practitioners

The UK Government's Government Response of 30 January 2026 confirms the Government will establish a voluntary, regulator-backed oversight regime for sustainability assurance providers, operated by the FRC:

• Interim regime targeted to be operational by mid-2026 — as at 27 July 2026 the FRC has not announced that the register is live, and statutory underpinning is to follow when Parliamentary time allows
  
• Voluntary registration — providers opt in; registration is not a precondition to providing sustainability assurance
  
• Profession-agnostic — covers both audit and non-audit professionals and firms
  
• Firms first — initial focus on registration of sustainability assurance firms over sole practitioners
  
• Broad scope — covers UK SRS, TCFD-aligned disclosures, EU ESRS under CSRD, and other ISSB-aligned standards
  
• Quality conditions — registration will initially verify skills and expertise, with quality management conditions built up over time

The DBT consultation on an oversight regime for sustainability assurance received 99 responses, with over 80% supporting the voluntary approach.

How assurance will work in practice from 1 January 2027

For the first reporting cycle under mandatory UK SRS S2 rules (accounting periods beginning on or after 1 January 2027):

Voluntary assurance commissioned where reporting entities choose. Many entities currently obtain voluntary assurance over their TCFD-aligned disclosures. Those with existing voluntary assurance practice typically continue it, applying ISSA (UK) 5000 to the new UK SRS disclosures.

Disclosure in the annual financial report regardless. Every in-scope listed company must include a statement under the FCA's paragraph 7.6 rule, whether assurance has been obtained or not.

Where assurance is obtained, the four-element disclosure under paragraph 7.7 follows. Most assurance reports already include the assurance level, standards used, and scope — preparing the disclosure is largely a matter of extracting that information.

Practitioner identification via the FRC register. The register is targeted to be operational by mid-2026 and is intended to let companies identify registered practitioners; it has not been confirmed as launched.

Limited vs reasonable assurance

ISSA (UK) 5000 supports both limited and reasonable assurance engagements:

Limited assurance: The practitioner performs less extensive procedures and obtains a meaningful but lower level of assurance. The conclusion is expressed in negative form — "nothing has come to our attention that causes us to believe that the disclosures have not been prepared in accordance with UK SRS."

Reasonable assurance: The practitioner performs sufficient procedures to obtain a high level of assurance. The conclusion is expressed in positive form — "in our opinion, the disclosures have been prepared in accordance with UK SRS."

Practitioner time and fees for reasonable assurance are substantially higher than for limited assurance. The market expectation is that voluntary limited assurance will be the norm in first reporting cycles, with reasonable assurance reserved for entities with mature systems and controls.

What audit committees should be asking now

Six questions audit committees at in-scope listed companies should be working through ahead of the first 1 January 2027 reporting year:

1. Will the company seek voluntary third-party assurance over its UK SRS S2 disclosures? Strategic decision driven by investor expectations, peer practice, existing assurance arrangements, and readiness of internal data and controls.

2. Who will provide the assurance — the statutory auditor or a separate sustainability assurance provider? Many entities choose the statutory auditor for synergy; others prefer a separate provider for independence.

3. At what level — limited or reasonable assurance? Limited assurance is the typical starting point.

4. What is the scope of the engagement? Whether assurance covers UK SRS S2 only, both S1 and S2, all material assertions, only quantitative metrics, Scope 1 and 2 but not Scope 3, etc.

5. What is the readiness of internal controls over sustainability information? Sustainability data infrastructure typically has weaker internal controls than financial data.

6. How will the company satisfy the CP26/5 paragraph 7.6 disclosure rule? Even if no assurance is obtained, the company must include a statement in the annual financial report.

Comparison with other jurisdictions

The EU CSRD position — mandatory limited assurance from the start — is the regime most often compared with UK SRS. The UK has chosen a different path: voluntary assurance with a disclosure rule about whether assurance was obtained.

The government has not published a decision, or a timetable for a decision, on whether UK sustainability assurance will ever be mandatory.

For multi-jurisdictional reporters, an entity required to obtain mandatory limited assurance under CSRD will typically already have most of the infrastructure to obtain voluntary limited assurance under UK SRS, and the two can often be combined in a single engagement.

Liability and the Strategic Report

Sustainability disclosures made under UK SRS within the Strategic Report attract the same section 463 safe-harbour protection as other Strategic Report disclosures. Section 463 limits directors' civil liability for statements made in the Strategic Report to circumstances where the director knew the statement was untrue or misleading, or was reckless, or where the statement involves dishonest concealment.

The Government's consultation response on UK SRS confirms that section 463 protection extends to UK SRS disclosures placed in the Strategic Report. Voluntary third-party assurance does not change this protection — it provides additional credibility for investors but does not transfer or alter directors' liability.

Frequently asked questions

Is third-party assurance mandatory under UK SRS?

No. FCA CP26/5 paragraph 7.5: "we are not proposing to set mandatory requirements for the assurance of sustainability reporting at this time."

When does mandatory assurance start?

There is no published date and no proposal to introduce one. CP26/5 does not propose mandatory assurance; the Government has said it is separately considering the longer-term approach to the operation and oversight of the sustainability assurance market.

Do listed companies have to obtain assurance over Scope 3 emissions?

No mandatory assurance applies. Where voluntary assurance is obtained over Scope 3 disclosures, that assurance must be specified in the annual financial report under paragraph 7.6.

What does ISSA (UK) 5000 cover?

General requirements for sustainability assurance engagements, applicable to both limited and reasonable assurance. Profession-agnostic. Effective for engagements on sustainability information reported for periods beginning on or after 15 December 2026.

When does the FRC register launch?

The Government Response tasked the FRC with having the interim register operational by mid-2026. As at 27 July 2026 there is no FRC announcement that the register is live, so treat mid-2026 as a target rather than a launch date. Registration is voluntary.

Will registration be required to provide UK SRS assurance?

No. Registration is voluntary. The register is intended to provide a public list of practitioners with demonstrated relevant skills; it will not gate market entry.

Does the statutory auditor have to provide UK SRS assurance?

No. The regime is profession-agnostic. The statutory auditor can provide UK SRS assurance if engaged, but it's a separate assurance engagement. Many entities will choose a separate sustainability assurance provider; others will appoint their statutory auditor.

How does this interact with EU CSRD assurance?

EU CSRD requires mandatory limited assurance. Groups with both UK SRS and CSRD obligations can typically combine engagement scopes, applying appropriate standards for each jurisdiction. The practical assurance work substantially overlaps.

Will the FCA mandate assurance in the future?

Unknown, and nothing published settles it. CP26/5 does not propose mandatory assurance, and no consultation on mandating it has been published.
What the Government has committed to is the voluntary FRC register, with statutory underpinning when Parliamentary time allows. Any suggestion that mandatory assurance is a settled direction of travel is commentary, not policy.

Where does liability sit for assured sustainability disclosures?

Companies Act 2006 section 463 safe-harbour applies to Strategic Report disclosures.
Voluntary third-party assurance does not change the section 463 protection. The assurance provider has its own contractual and professional liability for the assurance conclusion.