Sustainability assurance standards · ISSA (UK) 5000
ISSA (UK) 5000: the standard, paragraph by paragraph
ISSA (UK) 5000 is the UK’s sustainability assurance standard, issued by the Financial Reporting Council on 12 November 2025 for voluntary use.
It governs how an assurance engagement is performed, not whether one must be commissioned.
This page reads the paragraphs that decide what a UK SRS reporter will see in an assurance report.
What it is
A UK version of the IAASB’s ISSA 5000
The FRC called ISSA (UK) 5000 “a UK version of the global benchmark standard for sustainability assurance”, developed by the IAASB, and issued it for voluntary use by UK assurance providers.
The FRC’s conforming amendments say it adopts the text of ISSA 5000, so the paragraph numbers and the effective date match the international standard.
It deals only with attestation engagements (¶10): the company prepares the sustainability information, and the practitioner reports on it.
It deals with both reasonable and limited assurance engagements (¶9), and nothing in it requires one level rather than the other.
It is framework-neutral: it can be used on information prepared under UK SRS, the GHG Protocol, the ESRS or a company’s own criteria.
The FRC describes it as profession-agnostic, so it is not reserved to audit firms.
The obligation side — what companies must say about assurance — is on UK SRS assurance.
- 12 Nov 2024IAASB publishes ISSA 5000
The international standard.
- 17 Jan 2025IESBA releases the sustainability ethics standards
Now Part 5 of the IESBA Code.
- 29 May–31 Jul 2025FRC consults on a UK version
Feedback statement published with the standard.
- 12 Nov 2025FRC issues ISSA (UK) 5000
“For voluntary use” by UK assurance providers.
- 15 Dec 2026Effective
For periods beginning on or after this date.
Paragraph 15
The ISSA 5000 effective date, and what “effective” means
Paragraph 15 makes the standard effective for 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.
Earlier application is permitted.
For a calendar-year company, 2027 is the first year it is effective, and 2027 is also the first year the FCA’s UK SRS rules reach.
“Effective” is not “compulsory”.
Paragraph 20 says a practitioner shall not represent compliance with the standard unless it has complied with it, which is how the standard binds: by representation.
From the effective date, anyone who says an engagement was performed under ISSA (UK) 5000 is held to all of it.
The ethics standards move on the same date: the IESBA’s sustainability provisions apply to periods from 15 December 2026, with Sections 5405 and 5406 on value-chain component work from 1 July 2028.
Enter a period start or an as-at date in the panel and it tells you whether the standard is effective for it.
Effective-date check · ISSA (UK) 5000 ¶15
- EffectiveISSA (UK) 5000 is effective for this engagement (1 January 2027)A practitioner who says the engagement was performed under ISSA (UK) 5000 must comply with all of it. Nothing in UK law requires the engagement to be commissioned.ISSA (UK) 5000 ¶¶15, 20
- EthicsIESSA independence and ethics apply to the same periodsSections 5405 and 5406, on assurance work at value-chain components, apply only to periods beginning on or after 1 July 2028.ISSA (UK) 5000 ¶34; IESBA Code Vol 2 Part 5
- InternationalISAE 3410 no longer applies to GHG statements internationallyThe IAASB’s withdrawal of ISAE 3410 takes effect from ISSA 5000’s effective date.IAASB announcement, 8 May 2025
Effective does not mean required: no UK law or rule obliges any entity to obtain sustainability assurance.
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Paragraphs 18, 190 and 198
Two levels, two kinds of sentence
| Paragraph | What it says | Why a reader should care |
|---|---|---|
| ¶18(a) | Reasonable assurance reduces engagement risk to an acceptably low level; the conclusion conveys an opinion | The stronger form, and the rarer one |
| ¶18(b) | Limited assurance reduces risk to an acceptable level, greater than for reasonable; the level must still be “meaningful” | Meaningful means clearly more than inconsequential — not a formality |
| ¶190(c)(vi) | Reasonable: a positive statement; limited: whether a matter has come to attention | The grammar of the report tells you the level |
| ¶190(d)(ii) | A limited report must say its procedures are less extensive and its assurance substantially lower | The health warning is compulsory |
| ¶198L | Limited: “no matter(s) has come to the attention of the practitioner…” | Headed “Basis for Conclusion” |
| ¶198R | Reasonable: “…is prepared, in all material respects, in accordance with…” | Headed “Basis for Opinion” |
| ¶87 | No change to a lower level of assurance without a reasonable justification | A reasonable engagement cannot be quietly downgraded |
A limited assurance conclusion is a double negative by design.
It is never a statement that the data is correct, and the report itself must say its assurance is substantially lower than reasonable assurance.
The distinction matters in practice: the FRC’s market study found 83% of FTSE 350 assurance engagements in 2023 were limited.
Under the FCA’s rules, a listed company that obtains assurance says to what level each disclosure was assured (UKLR 6.6.6R(8)(d)).
How it meets UK SRS
What ISSA (UK) 5000 means for a UK SRS report
UK SRS S1 and S2 contain no assurance requirement.
The FCA’s final rules ask listed companies to state whether they obtained assurance and which standards were used, and the FCA said it considered stakeholders’ interest in ISSA (UK) 5000 but kept the rule standard-neutral “to maintain flexibility for issuers” (PS26/19).
So a company may report that its provider used ISSA (UK) 5000, ISAE (UK) 3000 or another standard, and names it.
The government’s oversight response had consulted on making ISSA (UK) 5000 a condition of joining a voluntary practitioner register, and gave no response on that question, leaving the design to the FRC (¶¶5.2, 5.9).
That register had not opened on the latest available record.
Which UK SRS disclosures are hardest to assure — Scope 3, scenario analysis, transition plans — is covered on UK SRS assurance; the climate standard itself is on UK SRS S2.
It exists — issued 12 November 2025.
It applies to those who choose it — from 15 December 2026.
It compels nobody — unless a future instrument says otherwise.
Paragraphs 11, 34 and 42
Who can perform it, and under which ethics
Paragraph 34 requires compliance with the provisions of the IESBA Code related to sustainability assurance engagements, with any more restrictive national requirements, or with requirements an appropriate authority has determined to be at least as demanding.
It does not point to the FRC Ethical Standard, whose introduction lists the audit and other public interest engagements it covers; sustainability assurance is not among them.
The FRC has not issued a separate UK ethical standard for sustainability assurance.
The IESBA says its sustainability ethics standards apply to all sustainability assurance practitioners regardless of background, so an engineering or certification firm can use the standard on the same terms as an audit firm.
Under those standards, a firm may not provide a non-assurance service to a public interest entity it assures if the service might create a self-review threat; for other clients it applies the conceptual framework.
Two UK changes to the international text
Paragraph 11 says a practitioner applying ISSA (UK) 5000 is not required to apply ISAE (UK) 3000 as well.
Paragraph 42 and A29 prohibit the use of internal auditors to provide direct assistance in an ISSA (UK) 5000 engagement, while allowing use of the internal audit function’s work where direct assistance is not given.
These are UK modifications; no published line-by-line comparison is relied on here to say they are the only ones.
What it replaces
ISAE 3410, ISAE 3000 and the transition
| Standard | Position | Source |
|---|---|---|
| ISSA 5000 (IAASB) | Published 12 November 2024; effective for periods from 15 December 2026 | IAASB |
| ISSA (UK) 5000 (FRC) | Issued 12 November 2025; effective for periods from 15 December 2026 | FRC |
| ISAE 3410 (IAASB) | Withdrawal takes effect from ISSA 5000’s effective date | IAASB, 8 May 2025 |
| ISAE (UK) 3000 (FRC) | Still listed as current; no UK withdrawal located | FRC |
In 2023, 69% of FTSE 350 sustainability assurance engagements referenced ISAE 3000, so most existing arrangements will meet the new standard at their next renewal.
Professional commentary on the change is collected by the ICAEW, including its notes on the UK SRS publication and on reporting and assurance in 2026.
For how assurance fits the UK SRS standards as a whole, start at the UK SRS hub.
Check your reading
Six questions on the standard
Each answer names the paragraph it comes from, so a wrong answer sends you to the text.
The questions cover the effective date, what makes the standard binding, ethics, the wording of a limited conclusion, downgrading, and the register.
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If you are deciding whether to commission assurance for a first UK SRS report, the decisions are set out on UK SRS assurance; you can also book a free 15-minute call.
Test the standard · six questions
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Frequently asked
Questions people ask
What is ISSA (UK) 5000?
International Standard on Sustainability Assurance (UK) 5000, General Requirements for Sustainability Assurance Engagements.
The Financial Reporting Council issued it on 12 November 2025 as the UK version of the IAASB’s ISSA 5000, for voluntary use by UK assurance providers.
It sets requirements for limited and reasonable assurance engagements on sustainability information.
When is ISSA (UK) 5000 effective?
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.
Earlier application is permitted (¶15).
Is ISSA (UK) 5000 mandatory?
Not for companies.
No UK law or rule requires sustainability assurance, and the FCA’s rules do not name any assurance standard.
The standard binds a practitioner who represents that it has complied with it (¶20).
What is the difference between ISSA 5000 and ISSA (UK) 5000?
The UK version adopts the IAASB text.
Its UK changes include that a practitioner applying it need not also apply ISAE (UK) 3000 (¶11), and a prohibition on using internal auditors to provide direct assistance (¶42, A29).
No line-by-line comparison has been published by the FRC that this page relies on, so it does not claim these are the only differences.
Does ISSA (UK) 5000 only apply to UK SRS?
No. It applies to assurance engagements on sustainability information generally, whatever framework the information was prepared under.
UK SRS disclosures are one kind of information it can be used for.
Which ethics rules apply to an ISSA (UK) 5000 engagement?
Paragraph 34 requires the provisions of the IESBA Code related to sustainability assurance engagements, with any more restrictive national requirements, or requirements an appropriate authority has determined to be at least as demanding.
It does not point to the FRC Ethical Standard, which is an audit standard.
Can non-accountants use ISSA (UK) 5000?
Yes.
The FRC describes the standard as profession-agnostic, and the IESBA’s sustainability ethics standards apply to all sustainability assurance practitioners regardless of background.
What does ISSA 5000 replace?
Internationally, the IAASB is withdrawing ISAE 3410, its greenhouse gas statements standard, from ISSA 5000’s effective date.
In the UK the FRC still lists ISAE (UK) 3000 and no UK withdrawal has been located.
Sources
Primary sources
Every figure, date and status on this page traces to the instrument’s owner.
Secondary commentary is never the source for a number.
- Financial Reporting CouncilISSA (UK) 5000 — General Requirements for Sustainability Assurance Engagements, ¶¶9–11, 15, 18, 20, 34, 42, 87, 190, 198, A29
Issued 12 November 2025; read at the paragraph.
- Financial Reporting CouncilFRC takes steps to support quality and consistency in sustainability assurance (12 November 2025)
“For voluntary use” by UK assurance providers.
- Financial Reporting CouncilAssurance standards — FRC library
“ISSA (UK) 5000 · Publication date 12 November 2025”; ISAE (UK) 3000 still listed.
- Financial Reporting CouncilRevised Ethical Standard 2024 — Introduction I1
- IAASBISSA 5000 — General Requirements for Sustainability Assurance Engagements (12 November 2024)
The international text ISSA (UK) 5000 adopts.
- IAASBIAASB announces withdrawal of ISAE 3410 (8 May 2025)
- IESBAInternational Ethics Standards for Sustainability Assurance (including International Independence Standards)
Part 5 of the IESBA Code; effective 15 December 2026, Sections 5405–5406 from 1 July 2028.
- Department for Business and TradeDeveloping an oversight regime for sustainability assurance — government response (30 January 2026)
Voluntary, opt-in register; interim regime tasked for mid-2026.
- Financial Conduct AuthorityPS26/19 — Aligning listed issuers’ sustainability disclosures with international standards (30 September 2026)
Final rules: comply or explain against UK SRS, UKLR 6, 14, 15, 16 and 22, periods from 1 January 2027.
- Financial Conduct AuthorityPS26/19 PDF — response on assurance and UKLR 6.6.6R(8)(d)
The FCA considered naming ISSA (UK) 5000 and chose not to.
- Department for Business and TradeUK Sustainability Reporting Standards: UK SRS S1 and UK SRS S2 (25 February 2026)
The publication page for both standards; voluntary for any entity.
- ICAEWGovernment publishes UK Sustainability Reporting Standards (February 2026)
Professional commentary — reading, not a source for any fact here.
- ICAEW2026: sustainability reporting and assurance (January 2026)
Professional commentary — reading only.