Limited or Reasonable? The Assurance Level UK REITs Buy for Their Carbon Data
2 November 2026 · 19 min read · Mian Khubaib Jim
None of 17 UK REITs buys reasonable assurance on Scope 3. Only 2.7% of assured tonnes sit at the higher assurance level. What changes from 2027.
The assurance level a landlord buys decides what an independent check of its carbon figures actually proves. Limited assurance says nothing has come to the attention of the provider. Reasonable assurance gives a positive opinion on the figure. This paper answers one question. Which assurance level do UK real estate investment trusts (REITs) buy for their carbon data and how much of their reported footprint does reasonable assurance cover? The answer comes from the latest assurance statements of 19 UK REITs. None of them buys reasonable assurance on Scope 3. Across the 12 that state their assured tonnes only 2.7% sit under reasonable assurance.
Of 17 UK REITs with an external check none buys reasonable assurance on Scope 3. See how Sustainify AI prepares carbon data for any assurance level with a trace from every figure to its source.
Summary of findings
The findings in six numbers
Number | What it shows |
|---|---|
17 of 19 | UK REITs examined that obtain some external review of their carbon data |
0 of 17 | REITs that buy reasonable assurance on any Scope 3 figure |
2 of 17 | REITs that buy reasonable assurance on Scope 1 and 2 (Unite and Big Yellow) |
2.7% | Share of assured tonnes under reasonable assurance across the 12 REITs that state them |
4.8% | Share of those assured tonnes that is Scope 1 and 2 and so the most reasonable assurance can reach while Scope 3 stays limited |
8 of 17 | Statements that cite ISAE 3410 which is withdrawn from 15 December 2026 |
Source. Assurance statements and company reports listed in Table 1. Calculations by this paper.
Limited assurance is the norm. Thirteen of the 17 REITs with an external review buy limited assurance on every carbon metric. One buys moderate assurance under AA1000AS. Two buy reasonable assurance on Scope 1 and 2 and limited assurance on Scope 3 [1] [2]. A certificate for one more REIT says reasonable while its own report says limited [3] [4].
The higher level reaches little of the footprint. Across 12 REITs the assured total is 1363595 tCO2e. Scope 3 is 95.2% of it. Scope 1 and 2 is 4.8%. Reasonable assurance covers 37419 tCO2e or 2.7%. For a landlord whose footprint is mostly tenant energy the choice of level for Scope 1 and 2 barely moves how much of the footprint is tested to a high standard.
The rules ask for disclosure and not for a level. The Financial Conduct Authority (FCA) final rules in PS26/19 require listed companies in scope to say whether they obtained assurance and from whom. The FCA does not mandate assurance [5]. The UK Government recorded no clear consensus on the end goal for the assurance level (paragraph 6.3) [6].
Why the assurance level matters for UK REITs
From accounting periods beginning on or after 1 January 2027 a listed commercial company in scope of PS26/19 must state whether it obtained third party assurance over its climate related disclosures and name the provider (UKLR 6.6.6R(8)(d)). The policy statement says the disclosure also covers the level and the standards used and where the report can be found (paragraph 2.45) [5]. These UK Sustainability Reporting Standard (UK SRS) disclosures succeed the TCFD aligned listing rules. Closed ended investment funds are outside the rules (paragraph 3.7) [5].
The assurance level therefore becomes a line that investors and lenders can compare. A finance director who signs a carbon figure needs to know whether it was tested or reviewed. A lender testing a carbon target in a loan needs to know the same. The question this paper answers is what UK REITs buy today and how much of the footprint that purchase covers.
Definitions
Limited assurance ends in a negative conclusion. The provider states that nothing has come to its attention to suggest the figures are materially misstated. Reasonable assurance ends in a positive opinion that the figures are fairly stated. It is the level of a financial audit. Moderate assurance is the term used by the AA1000 Assurance Standard (AA1000AS). An agreed upon procedures engagement reports factual findings and gives no assurance.
ISAE 3000 (Revised) and ISAE 3410 are the international standards most providers cite. ISAE 3410 covers greenhouse gas statements and is withdrawn from the effective date of ISSA 5000 which is periods beginning on or after 15 December 2026 [7]. ISO 14064 Part 3 is the verification standard used by many certification bodies. Materiality is the size of error a provider treats as significant.
F gas emissions are refrigerant leaks reported in Scope 1. Embodied carbon is the emissions from building materials and construction and often sits in Scope 3 Category 2. Gross and net calorific value are two bases for gas emission factors that give different figures from the same consumption. Each term is defined in the Sustainify AI glossary.
Method
The latest assurance or verification statement of 19 UK listed REITs or REITs listed until recently was read between 5 and 15 October 2026. Where a statement could not be opened the company description of the engagement was used and is labelled. For each REIT the provider and the standard and the level for Scope 1 and Scope 2 and Scope 3 were recorded together with any materiality threshold.
Twelve statements or matching reports state the assured Scope 1 and Scope 2 location based and Scope 3 tonnes. For those 12 the share of assured tonnes under each level was calculated. Landsec and British Land and Hammerson were left out of that calculation because their assured tonnes could not be confirmed. Safestore was left out because its tables do not mark which absolute figures were assured. Primary Health Properties was left out because its certificate and its report give different levels.
Findings
Finding 1. No REIT in the sample buys reasonable assurance on Scope 3
Table 1. Assurance level by REIT
REIT | Period | Provider | Standard cited | Scope 1 and 2 | Scope 3 |
|---|---|---|---|---|---|
Landsec [8] | Year to March 2026 | EY | ISAE 3000 (Revised) | Limited | Limited on all disclosed categories |
British Land [9] | Year to March 2026 | DNV | ISAE 3000 (Revised) and ISO/IEC 17029 | Limited | Limited |
SEGRO [10] | 2024 | SLR Consulting | ISAE 3000 and ISAE 3410 | Limited | Limited |
Derwent London [11] | 2025 | PwC | ISAE 3000 (Revised) and ISAE 3410 | Limited | Limited |
Great Portland Estates [12] | Year to March 2026 | PwC | ISAE 3000 (Revised) and ISAE 3410 | Limited | Limited on Category 13 sub metered supply |
Hammerson [13] | 2025 | BDO | ISAE 3410 | Limited | Limited |
LondonMetric [14] | 2025 | ISOS Group | AA1000AS v3 | Moderate | Moderate on Category 13 |
Shaftesbury Capital [15] | 2025 | Carbon Footprint Ltd | ISO 14064 Part 3 | Limited | Limited |
Workspace [16] | Year to March 2026 | Bureau Veritas | ISAE 3000 (Revised) and ISAE 3410 | Limited | Limited |
Unite [1] | 2025 | SGS | ISO 14064 Part 3 | Reasonable | Limited |
Big Yellow [2] | Year to March 2026 | SGS | ISAE 3000 (Revised) and ISO 14064 Part 3 | Reasonable | Limited |
Tritax Big Box [17] | 2025 | TÜV Rheinland | ISAE 3000 (Revised) and ISAE 3410 | Limited | Limited on Category 2 only |
Safestore [18] | Year to August 2025 | SLR Consulting | ISAE 3000 and ISAE 3410 | Limited on selected metrics | Not marked as assured |
Grainger [19] | Year to September 2025 | SE Advisory Services | ISO 14064 Part 3 | Limited | Limited |
Supermarket Income REIT [20] | Year to June 2026 | Grant Thornton | ISAE 3000 (Revised) and ISAE 3410 | Limited | Limited |
Primary Health Properties [4] [3] | 2025 | Achilles via Toitū Carbon Reduce | ISO 14064 Part 1 on the certificate | Reasonable on the certificate and limited in the report | Limited on the certificate |
Picton [21] | 2024 | JLL | ISAE 3000 (Revised) | Limited | Limited |
Custodian Property Income REIT [22] | Year to March 2026 | None | None | No third party assurance | No third party assurance |
Schroder REIT [23] | Year to March 2025 | EY | Agreed upon procedures under ISRS 4400 (Revised) on an ESG scorecard | No assurance | No assurance |
Source. Assurance statements and company reports as cited. The Derwent London and Hammerson and British Land statements were not read in full and the company description is used. Derwent London buys reasonable assurance on selected green finance metrics only.
Two REITs buy the higher level and both buy it from the same certification body. Unite states that the level agreed is reasonable for Scope 1 and 2 and limited for Scope 3 [1]. Big Yellow buys reasonable assurance on Scope 1 and 2 and energy and limited assurance on Scope 3 [2]. The pattern is not confined to REITs. The Financial Reporting Council (FRC) found that 83% of assurance engagements for FTSE 350 companies in 2023 involved limited assurance [24]. Two REITs buy no assurance at all. Custodian states that it does not conduct third party assurance [22]. Schroder REIT reports an agreed upon procedures engagement under ISRS 4400 (Revised) covering an ESG scorecard for two assets and not its carbon data [23]. That type of engagement reports factual findings and gives no assurance.
Finding 2. Reasonable assurance covers 2.7% of assured tonnes
The REITs that buy the higher level buy it where their footprint is smallest. For a landlord most emissions sit in Scope 3 and above all in tenant energy.
Table 2. Assured tonnes by scope and the level on Scope 1 and 2
REIT | Period | Scope 1 and 2 assured (tCO2e) | Scope 3 assured (tCO2e) | Level on Scope 1 and 2 | Scope 1 and 2 as share of assured tonnes |
|---|---|---|---|---|---|
Unite | 2025 | 35953 | 12079 | Reasonable | 74.9% |
Great Portland Estates | Year to March 2026 | 3270 | 2419 | Limited | 57.5% |
Workspace | Year to March 2026 | 6840 | 14220 | Limited | 32.5% |
Picton | 2024 | 2780 | 9626 | Limited | 22.4% |
Derwent London | 2025 | 4466 | 33283 | Limited | 11.8% |
Big Yellow | Year to March 2026 | 1466 | 25024 | Reasonable | 5.5% |
Shaftesbury Capital | 2025 | 1168 | 36304 | Limited | 3.1% |
Grainger | Year to September 2025 | 1455 | 52106 | Limited | 2.7% |
Tritax Big Box | 2025 | 524 | 36115 | Limited | 1.4% |
SEGRO | 2024 | 6971 | 921589 | Limited | 0.8% |
Supermarket Income REIT | Year to June 2026 | 186 | 50249 | Limited | 0.4% |
LondonMetric | 2025 | 388 | 105114 | Moderate | 0.4% |
Total | 12 REITs | 65467 | 1298128 | Reasonable on 37419 | 4.8% |
Source. Statements and reports as cited in Table 1 and the LondonMetric report for its tonnes [25]. Scope 2 and the leased asset electricity inside Scope 3 are location based. Scope 3 is the assured categories only. The totals for Unite and Big Yellow and SEGRO and Grainger and Shaftesbury Capital are added by this paper from the components printed in the source. All other calculations are by this paper.
SEGRO alone is 68% of the assured total. Without SEGRO reasonable assurance covers 8.6% of assured tonnes and Scope 1 and 2 is 13.4%. The median share of Scope 1 and 2 across the 12 is 4.3%. Big Yellow shows the pattern. Its reasonable assurance covers 1466 tCO2e while 25024 tCO2e of Scope 3 sit under limited assurance [2].
Finding 3. Audit firms sign 5 of the 17 statements
Table 3. Who provides the review
Provider type | REITs | Count |
|---|---|---|
Big Four audit firm | Landsec and Derwent London and Great Portland Estates | 3 |
Other audit firm | Hammerson and Supermarket Income REIT | 2 |
Certification body | British Land and Workspace and Unite and Big Yellow and Tritax Big Box and Primary Health Properties | 6 |
Consultancy | SEGRO and Safestore and Shaftesbury Capital and LondonMetric and Grainger and Picton | 6 |
Source. Table 1. Provider type assigned by this paper.
Audit firms sign 5 of the 17 statements or 29%. Big Four firms sign 3. Across the FTSE 350 the FRC found that the Big Four signed 40% of assurance engagements by number in 2023 [24]. Globally 687 of 1158 assurance reports on 2024 disclosures were signed by audit firms in a sample of 1400 companies [26]. Both reasonable engagements in this sample were signed by a certification body.
Finding 4. Statements say little about what was tested
Five of the 17 disclose a materiality threshold. Great Portland Estates and Workspace use 5% [12] [16]. Unite and Big Yellow use 5% for Scope 1 and 2 and 10% for Scope 3 [1] [2]. Tritax Big Box uses plus or minus 10% [17]. None of the statements read gives a sample size. Of the statements read in full only British Land names the sites visited [9]. The ISOS statement for LondonMetric records that no visit to the headquarters or the facilities of the company was conducted [14].
Scope exclusions are common. LondonMetric excludes refrigerant losses and mobile combustion and emergency generator fuel from its assured Scope 1 and excludes market based Scope 2. The statement gives alignment with the GRESB 2026 standard as the reason [14]. Tritax Big Box assures only Category 2 in Scope 3 which is mainly embodied carbon and excludes downstream leased assets [17]. Great Portland Estates assures Category 13 only for the electricity it sub meters to customers [12]. A reader has to read the scope before relying on the word assured.
Finding 5. The rules ask for disclosure and not a level
Table 4. What each regime asks of assurance
Regime | Assurance required | Level | Status as at 15 October 2026 |
|---|---|---|---|
SECR [27] | No. Recommended as best practice | None set | In force since 2019 |
FCA PS26/19 [5] | No. Disclosure of whether assurance was obtained and the provider and the level and standard | Either | Final. Periods beginning on or after 1 January 2027 |
UK assurance provider register [6] | No. Voluntary registration run by the FRC | No clear consensus on the end goal | Response published January 2026. Interim register targeted by mid 2026 and operational ahead of 1 January 2027 |
ISSA (UK) 5000 [28] | Not a requirement to assure | Limited or reasonable | Effective for periods beginning on or after 15 December 2026 |
EU CSRD [29] | Yes for companies in scope | Limited. The requirement to adopt reasonable assurance standards was removed | Limited assurance standard due by 1 July 2027 |
GRESB 2026 [30] | No. External review of energy and GHG and water and waste data is scored | Verification and assurance treated equally. Level not distinguished | 5.5 points across MR1 to MR4 |
Source. Regime texts as cited.
Respondents told the FCA that limited assurance would be more feasible than reasonable assurance (paragraph 2.59) [5]. The FCA concludes that this is not the appropriate time to introduce mandatory assurance and says it will keep the case under review (paragraphs 2.60 to 2.72) [5]. The EU removed the step to reasonable assurance under the Corporate Sustainability Reporting Directive (CSRD) to avoid an increase in the costs of assurance [29]. No regime a UK REIT reports under requires reasonable assurance on carbon data.
Finding 6. Research shows users treat the levels differently
Table 5. What peer reviewed papers say about assurance level and demand
Paper | Finding |
|---|---|
Hodge et al 2009 [31] | Neither the level of assurance nor the type of practitioner had a significant effect on user confidence on its own. Only the interaction of the two mattered. A top tier accounting firm raised confidence where the level was reasonable |
Sheldon and Jenkins 2020 [32] | In an experiment with 153 non expert report users the effect of firm performance on believability disappeared once assurance was provided. Limited assurance was enough to produce that effect |
Datt et al 2018 [33] | Across 5184 firm year observations in 44 countries 66% of firms received carbon assurance and firms with higher carbon risk were more likely to seek it |
Zhou et al 2016 [34] | Corporate governance moderates country level factors for both the demand for GHG assurance and the choice of provider |
Farooq and de Villiers 2017 [35] | A review of 50 articles found that sustainability assurance was voluntary in most jurisdictions as at 2017 and before the EU and UK rules that followed |
Source. Abstracts of the papers cited. Datt et al and Zhou et al study carbon and GHG assurance. The other three study sustainability assurance in general.
The literature supports two points for a REIT. Users respond to the level and the provider together rather than to either on its own. And a REIT with more carbon exposure is more likely to buy assurance in the first place.
In this sample reasonable assurance covers 2.7% of assured tonnes and none of Scope 3. Make your carbon data assurance ready for the level you choose before the provider arrives.
What this means in practice
Five actions before the first UK SRS assurance disclosure
1. Choose the level metric by metric
Reasonable assurance on Scope 1 and 2 is a proven choice in this sample. Unite and Big Yellow already buy it [1] [2]. Decide whether a lender or a remuneration target relies on a figure and set the level for that figure. A sustainability linked loan KPI is the clearest case.
2. Move the engagement to ISSA 5000
Eight of the 17 statements cite ISAE 3410 which is withdrawn from 15 December 2026 [7]. ISSA (UK) 5000 applies to periods beginning on or after that date [28]. Agree the standard in the next engagement letter.
3. Ask for materiality and extent to be stated
Twelve of the 17 statements give no materiality threshold. Ask for the threshold and the number of entries and sites tested to be stated in the report.
4. Close the scope gaps before the provider arrives
Check that refrigerant F gas losses and embodied carbon are inside the boundary you want assured. State whether gas is priced on gross or net calorific value. Record any restatement of a prior year before the engagement starts.
5. Prepare the disclosure line now
PS26/19 asks for the provider and the level and the standard and where the report sits [5]. Write that line for the current year and check that it describes what was bought.
How Sustainify AI supports assurance
Carbon data lineage traces each figure to the entries and factor set and source file behind it so a provider can follow the audit trail. Carbon data governance locks closed periods so a prior year cannot move without a recorded restatement. The free Audit Readiness Check asks six questions about how your carbon data is produced. The platform supports the engagement. It does not replace an assurance provider.
Disclosure of interest. This paper is published by Sustainify AI. The analysis used the public sources and the method set out in the Method section and was carried out independently of the platform.
Limitations
The sample is small and mixed. Nineteen REITs were chosen by the writer. Periods run from 2024 to the year to June 2026. Three statements were not read in full and the company description is used.
Assured tonnes are not like for like. Each REIT assures different Scope 3 categories. SEGRO covers all geographies and dominates the total. Its assured Scope 3 figure uses location based electricity for leased assets and would be 732445 tCO2e on a market based basis [10]. Unite assures a limited set of Scope 3 categories.
One level is unresolved. Primary Health Properties holds a CarbonReduce certificate valid from 5 June 2026 that grades Scope 1 and 2 as reasonable and Scope 3 as limited [3]. Its own report describes 2024 as limited assurance and 2025 as pending limited assurance after an audit in March 2026 [4]. It is excluded from the counts of reasonable assurance and from Table 2.
Rule wording was partly read. The FCA rule text on level and standard was read in the policy statement narrative and not in the rule itself. The government response targets an interim voluntary register ahead of 1 January 2027. Whether it opened on that timetable was not checked.
What not to conclude. Limited assurance is not worthless and a REIT that buys it has not misreported. Reasonable assurance on Scope 1 and 2 is not a sign that the whole footprint was tested.
References
[1]SGS United Kingdom Ltd. ISO 14064 GHG Data Verification Statement The Unite Group PLC 2025. 9 February 2026. Accessed 15 October 2026.
[2]SGS United Kingdom Ltd. Assurance Statement on Selected KPIs Big Yellow Group PLC 2025/26. 8 May 2026. Accessed 15 October 2026.
[3]CarbonReduce certification programme. Certificate 2026138J Primary Health Properties PLC. Valid from 5 June 2026 to 5 June 2029. Accessed 15 October 2026.
[4]Primary Health Properties PLC. Responsible Business Report 2025. Page 10. Accessed 15 October 2026.
[5]Financial Conduct Authority. PS26/19 Aligning listed issuers sustainability disclosures with international standards. 30 September 2026. Paragraphs 2.45 and 2.51 and 2.59 and 2.60 and 2.72 and 3.6 and 3.7 and 3.12 and rule UKLR 6.6.6R(8)(d). Accessed 15 October 2026.
[6]Department for Business and Trade. Developing an oversight regime for assurance of sustainability related financial disclosures government response to consultation. 30 January 2026. Paragraph 6.3 and the section on the interim register. Accessed 15 October 2026.
[7]International Auditing and Assurance Standards Board. IAASB Announces Withdrawal of ISAE 3410 Assurance Engagements on Greenhouse Gas Statements. 8 May 2025. Accessed 15 October 2026.
[8]Ernst and Young LLP. Independent Limited Assurance Report to the Directors of Land Securities Group plc. 13 May 2026. Pages 1 and 2. Accessed 15 October 2026.
[9]The British Land Company PLC. Reporting Criteria and Independent Assurance 2026. DNV statement. Accessed 15 October 2026.
[10]SLR Consulting Limited. ISAE 3000 Assurance Statement SEGRO plc 1 January 2024 to 31 December 2024. 4 February 2025. Accessed 15 October 2026.
[11]Derwent London plc. Responsibility Report 2025. Pages 11 and 18 and 22. Accessed 15 October 2026.
[12]PricewaterhouseCoopers LLP. Independent Limited Assurance Report to the Directors of Great Portland Estates plc. 8 May 2026. Accessed 15 October 2026.
[13]Hammerson plc. ESG Report 2025. Page 35. Accessed 15 October 2026.
[14]ISOS Group. Independent Assurance Statement LondonMetric Property plc 2026. 29 June 2026. Accessed 15 October 2026.
[15]Shaftesbury Capital PLC. 2025 EPRA Sustainability Data Report. Appendix 3 Carbon Footprint Ltd statement of verification on page 33. Accessed 15 October 2026.
[16]Bureau Veritas UK Ltd. Independent Assurance Report to the Stakeholders of Workspace Group Plc. 25 June 2026. Accessed 15 October 2026.
[17]TÜV Rheinland UK Ltd. Greenhouse Gas Verification Statement Tritax Big Box REIT plc 2025. 3 February 2026. Page 2. Accessed 15 October 2026.
[18]Safestore Holdings plc. Mandatory Greenhouse Gas Emissions Report 2025. Year to 31 August 2025. Accessed 15 October 2026.
[19]Grainger plc. FY25 GHG Emissions Verification Statement. November 2025. Accessed 15 October 2026.
[20]Grant Thornton UK LLP. Limited Assurance Report Supermarket Income REIT plc FY26. 15 September 2026. Accessed 15 October 2026.
[21]Picton Property Income Limited. Sustainability Data and Performance Report. Calendar 2024 data. JLL statement on pages 33 and 34. Accessed 15 October 2026.
[22]Custodian Property Income REIT plc. EPRA sBPR Disclosures. Accessed 15 October 2026.
[23]Schroder Real Estate Investment Trust Limited. Annual Report and Consolidated Financial Statements 2025. Page 33. Accessed 15 October 2026.
[24]Financial Reporting Council. Assurance of Sustainability Reporting Market Study Final Report. 5 February 2025. Paragraphs 13 and 18 and 38. Accessed 15 October 2026.
[25]LondonMetric Property plc. Responsible Business and ESG Report 2026. Pages 7 and 25. Accessed 15 October 2026.
[26]International Federation of Accountants and AICPA and CIMA. The State of Play Sustainability Disclosure and Assurance 2019 to 2024. 2026. Page 11. Accessed 15 October 2026.
[27]Department for Business Energy and Industrial Strategy. Environmental Reporting Guidelines Including Streamlined Energy and Carbon Reporting Requirements. March 2019. Section on external verification or assurance. Accessed 15 October 2026.
[28]Financial Reporting Council. ISSA (UK) 5000 General Requirements for Sustainability Assurance Engagements. 12 November 2025. Paragraph 15. Accessed 15 October 2026.
[29]European Parliament and Council. Directive (EU) 2026/470 of 24 February 2026. Official Journal 26 February 2026. Recital 5 and Article 1(3). Accessed 15 October 2026.
[30]GRESB. 2026 Real Estate Assessment MR2 External Review of GHG Data. Indicators MR1 to MR4. Accessed 15 October 2026.
[31]Hodge K and Subramaniam N and Stewart J. Assurance of sustainability reports Impact on report users confidence and perceptions of information credibility. Australian Accounting Review. Volume 19 issue 3 pages 178 to 194. 2009. Accessed 15 October 2026.
[32]Sheldon MD and Jenkins JG. The influence of firm performance and (level of) assurance on the believability of managements environmental report. Accounting Auditing and Accountability Journal. Volume 33 issue 3 pages 501 to 528. 2020. Accessed 15 October 2026.
[33]Datt R and Luo L and Tang Q and Mallik G. An international study of determinants of voluntary carbon assurance. Journal of International Accounting Research. Volume 17 issue 3 pages 1 to 20. 2018. Accessed 15 October 2026.
[34]Zhou S and Simnett R and Green W. Assuring a new market The interplay between country level and company level factors on the demand for greenhouse gas (GHG) information assurance and the choice of assurance provider. Auditing A Journal of Practice and Theory. Volume 35 issue 3 pages 141 to 168. 2016. Accessed 15 October 2026.
[35]Farooq MB and de Villiers C. The market for sustainability assurance services A comprehensive literature review and future avenues for research. Pacific Accounting Review. Volume 29 issue 1 pages 79 to 106. 2017. Accessed 15 October 2026.
None of the regimes a UK REIT reports under requires reasonable assurance yet. Keep every figure traceable so your GHG assurance can move up a level when the market does.
Frequently Asked Questions
What is the difference between limited and reasonable assurance?
Limited assurance ends in a negative conclusion that nothing came to the attention of the provider. Reasonable assurance gives a positive opinion that the figures are fairly stated. It is the level of a financial audit.
Which assurance level do UK REITs buy?
In this sample 13 of 17 REITs with an external review buy limited assurance on every carbon metric. Two buy reasonable assurance on Scope 1 and 2 [1] [2]. None buys reasonable assurance on Scope 3.
How much of a REIT footprint does reasonable assurance cover?
Across 12 REITs reasonable assurance covers 2.7% of assured tonnes. Scope 1 and 2 is only 4.8% of the assured total so that is the most it could reach while Scope 3 stays limited.
Does PS26/19 make assurance mandatory?
No. Listed commercial companies in scope must say whether they obtained assurance and name the provider. The FCA says it does not consider it the right time to mandate assurance [5].
Which standard should a REIT use after 2026?
ISAE 3410 is withdrawn from 15 December 2026 [7]. ISSA (UK) 5000 applies to periods beginning on or after that date [28].
Does SECR require assurance?
No. The guidelines recommend it as best practice [27]. SECR reporting still has to state the method behind each figure.
Does GRESB reward reasonable assurance?
GRESB scores external review of energy and GHG and water and waste data across MR1 to MR4 [30]. It treats verification and assurance equally and its published scoring does not distinguish the level. The GRESB submission page covers the evidence you have to retain.
Who provides assurance to UK REITs?
In this sample Big Four firms sign 3 of 17 statements. Certification bodies and consultancies sign 12 and other audit firms sign 2.
Will CSRD require reasonable assurance?
No. The EU removed the requirement to adopt reasonable assurance standards. A limited assurance standard is due by 1 July 2027 [29]. CSRD reporting applies only to companies in scope.
What should a REIT prepare before an assurance engagement?
A trace from each figure to its source and the factor set behind it and a record of any restatement. Carbon assurance readiness starts there.