UK sustainability reporting transitions from voluntary to mandatory over three years.
Climate disclosures (UK SRS S2) start January 2027 for 500 listed companies,
followed by Scope 3 comply-or-explain in 2028 and broader sustainability disclosures in 2029.

Voluntary adoption (February 2026 onwards)

Any UK entity may adopt UK SRS from 25 February 2026.
Voluntary adopters must apply standards in full without transitional reliefs.
UK SRS S2 satisfies existing Companies Act climate disclosure requirements.

Phase 1 — UK SRS S2 proposed mandatory (1 January 2027)

Under the proposals in CP26/5 paragraph 3.4, UK SRS S2 climate disclosures become mandatory for accounting periods beginning on or after 1 January 2027 for in-scope listed companies.
The Cost Benefit Analysis confirms that the proposals "will impact around 500 listed companies."

460 UK commercial companies report fully against UK SRS S2.
40 international issuers follow transparency regime disclosing home-country standards.

First mandatory UK SRS S2 reports publish in spring 2028 for December 2027 year-ends.
Disclosure depth exceeds TCFD requirements with mandatory scenario analysis and financial statement connectivity.

Non-calendar year-ends

Companies with periods beginning before 1 January 2027 may continue TCFD reporting or adopt UK SRS early.

Periods beginning on or after 1 January 2027 but before 1 January 2028 (paragraph 8.12). The company must comply with the new UK SRS-aligned rules — or "explain" where permitted — unless it opts to make use of the transitional reliefs in UK SRS itself. The Scope 3 one-year deferral and UK SRS S1 two-year deferral apply from the date of initial application, not from a fixed calendar date.

Periods beginning on or after 1 January 2028 but before 1 January 2029 (paragraph 8.14). Same as the prior cohort, with the Scope 3 climate transitional relief no longer available (it expires after one year of initial application).

Excluded categories

Investment funds, shell companies, debt securities, and derivatives are excluded.
FCA may extend scope in future rule iterations.

Scope 3 comply-or-explain (January 2028)

Scope 3 value chain emissions become comply-or-explain from 1 January 2028.
Companies must disclose data or explain omissions with remediation steps.
See Scope 3 under UK SRS for category details.

UK SRS S2 incorporates December 2025 ISSB reliefs for financed emissions methodology flexibility
and jurisdictional measurement alternatives.

Broader sustainability comply-or-explain (January 2029)

UK SRS S1 non-climate topics (biodiversity, water, workforce, supply chain)
move to comply-or-explain from 1 January 2029.
S1 conceptual foundations apply from 2027 alongside S2.

Modernising Corporate Reporting: the second wave

CP26/5 only covers listed issuers. The Government has separately confirmed in the DBT consultation response (paragraph 1.16) that the question of mandatory UK SRS for private companies will be addressed through the Modernising Corporate Reporting (MCR) programme, announced in October 2025. The MCR consultation is expected later in 2026.

The MCR programme has two distinct strands.

Strand one — reporting reductions for medium-sized private companies. Set out in the Written Ministerial Statement of 21 October 2025, this strand introduces three legislative changes:

• Most medium-sized private companies exempted from the Strategic Report requirement
• Wholly-owned subsidiaries exempted from the Strategic Report where they are covered by a UK parent's group report
• The Directors' Report requirement removed for all companies, with useful provisions (including SECR-style energy and emissions reporting) relocated elsewhere

The Government estimates these reforms will benefit up to 44,000 medium-sized private companies and 7,000 subsidiary companies, and remove the Directors' Report requirement from approximately 440,000 companies — saving UK businesses around £230 million per year in administrative costs.

Strand two — extending UK SRS to economically significant private companies. The DBT consultation response paragraph 1.16 confirms this will be addressed within the broader MCR consultation. Three issues that the consultation must resolve:

• Defining "economically significant." Paragraph 1.61 of the DBT response records that respondents asked for a clear definition. The current best estimate is that the threshold will resemble the existing Companies (Strategic Report) (Climate-related Financial Disclosure) Regulations 2022 threshold — more than 500 employees and more than £500m turnover — but this is not confirmed.
• Subsidiary exemptions. Paragraph 1.67 records strong respondent support for an exemption where a parent company already reports against UK SRS or an equivalent international standard (such as ESRS).
• Phasing and proportionality. Paragraph 1.68 records that "proportionality is the priority for consultation respondents" and that a phased approach with a longer preparation period is expected.

For practical planning purposes: the earliest realistic effective date for any private company UK SRS regime is 2028 reporting periods, and depending on the consultation timeline could be later. See UK SRS for private companies for the detailed cohort analysis.

Assurance: ISSA (UK) 5000 effective from 15 December 2026

UK SRS does not mandate third-party assurance. CP26/5 proposes a disclosure obligation on whether assurance has been obtained, the level (limited or reasonable), the standards used, and the identity of the assurance provider — but not a requirement to obtain assurance.

The FRC's parallel work has produced the UK version of the International Standard on Sustainability Assurance — ISSA (UK) 5000, published on 12 November 2025. Key facts:

• Effective: for periods beginning on or after 15 December 2026
• Voluntary use only — not mandated by either the FRC or the FCA
• Profession-agnostic — applies to professional accountants and other practitioners who meet the relevant quality management and ethical requirements
• Both limited and reasonable assurance supported
• Aligned with the international IAASB standard — only one UK-specific modification, a safeguard preventing internal auditors from directly assisting in sustainability assurance engagements
• Consultation history: opened 29 May 2025, closed 31 July 2025; feedback paper and final standard both published 12 November 2025

The combination of ISSA (UK) 5000 effective December 2026, UK SRS S2 proposed mandatory January 2027, and CP26/5's voluntary-assurance disclosure obligation means the assurance market is taking shape now. In-scope listed companies should expect investor and audit committee questions on whether they intend to obtain voluntary assurance from 2027 onwards.

Full chronological timeline

What to do this year

Three things in-scope listed companies should be doing in 2026:

1. Run a gap analysis against UK SRS S2. Most TCFD-aligned reporters will find that the governance pillar (Pillar 1) and risk management pillar (Pillar 3) carry over with limited change. The step changes are concentrated in three areas: the quantitative climate scenario analysis required by paragraph 22 (see climate scenario analysis under UK SRS); the financial-statements connectivity required throughout the standard; and the cross-industry climate metrics in Appendix B, which include items most TCFD-aligned reports have not previously quantified.

2. Start the Scope 3 data conversation early. Even with the one-year Scope 3 carve-out, value-chain emissions data takes 12-18 months to collect and validate to audit-grade. Identify which Scope 3 categories are material now; engage the largest 20-30 value chain partners; pilot a calculation method. The December 2025 ISSB amendments allow some financial-sector entities to limit Scope 3 Category 15 to financed emissions, which simplifies the position for banks, insurers and asset managers — but only if the financed-emissions methodology is itself ready.

3. Decide on assurance. UK SRS does not mandate third-party assurance, but CP26/5 proposes a disclosure on whether assurance has been obtained. With ISSA (UK) 5000 effective from 15 December 2026, the voluntary-assurance market is forming. Audit committees should expect investor questions on assurance intent from the 2027 reporting cycle onwards.

For listed companies in UKLR 14 (secondary listing) and UKLR 15 (depositary receipts), the work is different: identify the climate and sustainability reporting standards applicable in the primary listing jurisdiction, confirm any reliefs claimed under those standards, and identify any voluntarily adopted standards. The FCA's transparency-focused regime requires disclosure of what already applies, not new UK reporting.

Frequently asked questions

Is UK SRS S2 proposed mandatory yet?

Not yet. UK SRS S2 was published on 25 February 2026 and is available for voluntary adoption. The FCA's CP26/5 consultation, which closed on 20 March 2026, proposes making it mandatory for in-scope listed companies for accounting periods beginning on or after 1 January 2027. The final FCA Policy Statement is expected in autumn 2026.

How many companies are in scope?

Approximately 500 listed companies, per CP26/5 Annex 2 paragraph 2 (the Cost Benefit Analysis). The breakdown is roughly 475 in the mandatory categories (UKLR 6 commercial companies, UKLR 16 non-equity, UKLR 22 transition) plus approximately 40 in the secondary listing category (UKLR 14) and a small number in depositary receipts (UKLR 15) — the latter two subject to a transparency-focused regime rather than direct UK SRS reporting.

Which UKLR categories are not in scope?

Six categories are excluded: closed-ended investment funds (UKLR 11), open-ended investment companies (UKLR 12), shell companies (UKLR 13), debt and debt-like securities (UKLR 17), securitised derivatives (UKLR 18), and warrants, options and miscellaneous securities (UKLR 19). For UKLR 11 and 12, the FCA's view is that reporting should fall on the asset manager rather than the fund; for the others, the FCA considers that direct reporting would not be proportionate or effective at this stage.

What about non-calendar year-ends?

CP26/5 paragraph 8.10 addresses listed companies whose accounting period begins before 1 January 2027 — they may either continue with TCFD-aligned rules for that period or voluntarily apply UK SRS early. For periods beginning on or after 1 January 2027 but before 1 January 2028 (paragraph 8.12), the new UK SRS-aligned rules apply, with transitional reliefs available under the standards themselves. The Scope 3 one-year deferral runs from the date of initial application, not from a fixed calendar date.

Will UK SRS replace TCFD reporting?

For in-scope listed companies, yes, once CP26/5 rules take effect from 1 January 2027. UK SRS S2 incorporates the four TCFD pillars and goes further on quantitative climate scenario analysis, financial-statements connectivity, and cross-industry metrics. The TCFD itself was disbanded in 2023 with monitoring responsibilities transferred to the ISSB. SECR (energy and emissions reporting under the Companies Act) is a separate regime that continues; the Government has signalled an intent to reduce duplication between SECR and UK SRS but no specific changes have been confirmed.

What is the Scope 3 carve-out and when does it expire?

CP26/5 paragraph 8.6 proposes that companies in scope can omit Scope 3 greenhouse gas emissions disclosures in their first year of mandatory UK SRS S2 reporting. For accounting periods beginning on or after 1 January 2028, Scope 3 reporting moves to comply-or-explain across all 15 GHG Protocol categories where material. The December 2025 ISSB amendments permit financial-sector entities to limit Scope 3 Category 15 to financed emissions as defined in UK SRS S2 — a meaningful simplification for banks, insurers and asset managers.

When does UK SRS S1 become mandatory?

UK SRS S1 non-climate disclosures move to comply-or-explain from accounting periods beginning on or after 1 January 2029. The S1 conceptual foundations — definitions of materiality, scope of the value chain, financial-statement connectivity, safe-harbour provisions — apply from January 2027 alongside UK SRS S2, because S2 cannot be applied without them. Full mandatory application of UK SRS S1 is subject to an FCA review point after the initial period.

What about private companies?

CP26/5 only covers listed issuers. The Government plans a separate consultation, expected later in 2026, on extending UK SRS to economically significant private companies through the Companies Act 2006 — within the broader Modernising Corporate Reporting programme. Size thresholds and application dates are not yet set; the earliest realistic effective date for any private company UK SRS regime is 2028 reporting periods.

Is sustainability assurance mandatory under UK SRS?

No. CP26/5 proposes only a disclosure obligation on whether assurance has been obtained, the level, the standards used, and the provider. The FRC published ISSA (UK) 5000 — the UK sustainability assurance standard — on 12 November 2025, effective for periods beginning on or after 15 December 2026, but its use is voluntary.