In short: Sustainability disclosures are only as good as the data behind them. Assurance is moving from voluntary to expected: ISSA 5000, the global sustainability assurance standard, applies to engagements on information for periods beginning on or after 15 December 2026, CSRD reporters need limited assurance, and the UK is setting up an oversight regime for sustainability assurance providers. TaxDigit's sustainability team selects the ESG metrics that matter to your audience, builds data processes with owners and an audit trail, designs internal controls and prepares the evidence an assurance provider will ask for. The assurance opinion itself is given by an independent provider.
From scattered spreadsheets to assurance-ready ESG data
ESG data usually comes from many systems and owners: meters, fleet cards, HR and payroll, procurement, facilities and suppliers, in formats from ERP exports to emails. The fix is the same as in financial reporting: one data policy, named owners, a single source of truth, documented methods and estimates, cut-off rules, and controls that prevent and detect errors. Primary data is preferred; proxies are acceptable when they are flagged, sanity-checked and replaced over time.
Good data also pays for itself. It supports benchmarking against peers, better ESG ratings, cheaper finance, and decisions about where to invest. Finance teams are the natural custodians: accuracy, completeness, consistency, timeliness and validity are already their job for the financial statements.
- Groups facing first assuranceCSRD reporters and companies seeking voluntary assurance on UK SRS disclosures.
- Finance and sustainability teamsBringing ESG data under the same discipline as financial data.
- Companies with ESG ratingsImproving data behind CDP, MSCI, S&P and other ratings.
- Boards and audit committeesUnderstanding the controls and risks in sustainability reporting.
Led by Dr Attieh Moezoddin, Head of Sustainability & ESG Advisory (PhD, Built Environment)Reviewed by Amir Rafiei, ACCA Certificate in Sustainability for FinanceLast reviewed
What we do
Choosing ESG KPIs
Environmental, social and governance metrics chosen for your audience, regulation, financial materiality and international goals, with clear definitions.
Data lifecycle design
Sourcing, collection, analytics and reporting steps with owners, timetables and a documented data trail.
Internal control framework
Preventive and detective controls over ESG data, automated where possible, mapped to the risks of misstatement.
ISSA 5000 pre-assurance
A mock assurance review: we test evidence, methods and controls the way an assurance provider would and fix the gaps first.
Errors and changes
Policies for restating prior years and base years after errors, method changes or acquisitions.
Dashboards and benchmarking
ESG dashboards, peer benchmarking and climate value-at-risk analysis for management and the board.
Qualities of decision-useful ESG data
| Quality | What it means in practice |
|---|---|
| Relevant | Material to the users' decisions; chosen for the audience |
| Faithful representation | Complete, neutral and free from error, including bad news |
| Comparable and consistent | Same methods year to year and close to peers' methods |
| Verifiable | A data trail from disclosure back to source, so another person reaches the same result |
| Timely | Available in time for the reporting timetable |
| Understandable | Clear definitions, methods, assumptions and boundaries disclosed alongside the metric |
ISSA 5000 is effective for assurance engagements on sustainability information for periods beginning on or after 15 December 2026, and supports both limited and reasonable assurance.
How an assurance readiness project runs
Current challenges, gaps, systems and stakeholders.
Metrics, targets, data requirements and owners.
Capture, cleanse, validate and store the data with controls.
Track performance, benchmark and get ready for assurance.
A dedicated sustainability and ESG team
TaxDigit has a dedicated sustainability and ESG team, led by Dr Attieh Moezoddin, Head of Sustainability & ESG Advisory. Attieh holds a PhD in the Built Environment from the University of Salford and is a sustainable development researcher whose doctoral work built a framework for sustainable urban development using expert panels and multi-criteria analysis (fuzzy Delphi, fuzzy AHP and fuzzy TOPSIS) across social, environmental, economic and cultural pillars.
Finance, reporting and tax quality is reviewed by Amir Rafiei, Senior Manager for Global Tax Strategy, Transfer Pricing and Sustainability, who holds the 
ACCA Certificate in Sustainability for Finance. The team works side by side with our accounts, tax, payroll and international specialists, so your sustainability disclosures, financial statements and tax returns rest on one set of facts. Statutory audit is carried out separately by our alliance firm Jelveh Audit & Assurance.
- PhD, Built Environment
- Sustainable development research
- Materiality and expert panels
- SDGs and impact
- Climate risk and reporting
- ESG metrics and analytics
- IFRS S1, S2 and UK SRS
- CSRD and ESRS
- CBAM and green taxes
All sustainability and ESG services
See the full overview on our sustainability and ESG services page, or go straight to a related service. Large groups may also need our large and multinational group tax support.
Official sources
Rules, thresholds and dates on this page were checked against these sources on 14 November 2026. We re-check them whenever they change.
Frequently asked questions
What is ISSA 5000?
The International Standard on Sustainability Assurance issued by the IAASB. It is framework-neutral, covers limited and reasonable assurance, and applies to engagements for periods beginning on or after 15 December 2026.
Do UK companies need sustainability assurance?
The FCA rules for listed companies do not require it, but many companies obtain it voluntarily, CSRD reporters must obtain limited assurance, and the UK is creating an oversight regime for sustainability assurance providers.
Does TaxDigit give the assurance opinion?
No. We prepare you for assurance. The opinion must come from an independent assurance provider. We coordinate with the provider you appoint.
What is the difference between limited and reasonable assurance?
Limited assurance gives a negative-form conclusion based on fewer procedures. Reasonable assurance gives a positive opinion based on more extensive work, closer to an audit.
Which ESG metrics should we report?
Those material to your users, required by regulation, relevant to financial performance and aligned with international goals. Common examples include GHG emissions, energy, water, waste, health and safety, gender pay gap and board composition.
Is primary data always required?
Primary data is preferred. Proxies and estimates can be used where data is missing, provided they are reasonable, flagged as uncertain, documented and improved over time.
Should ESG data be collected centrally or locally?
Central collection gives consistency; local calculation helps sites own and improve their numbers. Many groups use local collection with central review and controls.
Can you help improve our ESG ratings?
Yes. Better data and clearer disclosure often improve CDP and other ratings. We review the questionnaires and the evidence behind each answer.