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Sustainability Assurance

Strengthen the integrity of your sustainability data, build confidence in disclosures and support better decision-making.

Sustainability information increasingly influences procurement decisions, investment, financing, board oversight and external reporting.

Before publishing, organisations need confidence that their information is supported by appropriate evidence, documented methodologies, clear reporting criteria and effective controls.

Acclaro provides independent, risk-based limited assurance across greenhouse gas emissions, environmental metrics and wider sustainability reporting. Our objective is not only to issue an assurance conclusion. We also help organisations identify where reporting processes, evidence and controls need to improve so future reporting becomes more reliable, efficient and easier to assure.

Why this matters

Weak sustainability reporting processes can lead to repeated assurance queries, delayed reporting, inconsistent disclosures, higher assurance costs and reduced confidence from boards, customers and investors.

Strengthening the evidence, controls and methodologies behind the information helps organisations improve both external reporting and the quality of information used for internal decision-making.

Common sustainability assurance challenges

Many organisations are reporting emissions and sustainability metrics, but the underlying data, methodologies and controls are not always ready for independent review.

Common challenges include:

Incomplete or inconsistent activity data across sites, entities or business units;
Reliance on estimates, proxies and third-party information, particularly for Scope 3
Limited documentation of methodologies, assumptions and reporting boundaries
Fragmented systems, manual processes and weak data controls
Unclear ownership, review responsibilities and evidence trails
Growing scrutiny from customers, investors, regulators and rating platforms.

The challenge is not only producing the disclosure. It is ensuring that the underlying information can withstand independent challenge and is reliable enough to support reporting, governance and business decisions.

How organisations build stronger sustainability reporting

Organisations are at different stages of reporting maturity. Our services provide a practical progression from readiness, through to independent assurance and future improvement.

We identify data, methodology, evidence and control gaps before formal assurance begins.

This is suited to organisations preparing for first-time assurance, responding to customer requests, improving reporting quality or seeking to reduce disruption during future testing.

Typical activities include:

Reviewing reporting boundaries, data sources and ownership
Assessing methodologies, assumptions and emission factors
Mapping evidence trails and identifying documentation gaps
Reviewing data controls, review points and consolidation processes
Performing selected dry-run testing before formal assurance

We provide independent limited assurance over agreed sustainability information, data or metrics.

This may include:

Scope 1, Scope 2 and agreed Scope 3 emissions
Energy, waste and operational performance metrics
Selected sustainability-related KPIs
Reporting methodologies, assumptions and calculation approaches
Climate-related metrics, targets and selected disclosures
Underlying reporting processes, controls and evidence

The exact scope is agreed in advance and depends on the reporting criteria, intended use, evidence available and assessed risk.

We help organisations respond to assurance findings, strengthen controls and improve the efficiency of future reporting cycles.

This can include:

Prioritising assurance findings and management observations
Strengthening evidence retention and documentation
Improving data controls, ownership and review processes
Updating methodologies and assumptions logs
Preparing for repeat or broader assurance
Reviewing progress against agreed improvement actions

Our sustainability assurance approach

Our work is designed around five practical questions:

Agree the reporting boundary, reporting period, metrics, reporting criteria and intended use of the assurance output.

Review how sustainability information is collected, calculated, reviewed and reported.

Identify areas where information may be incomplete, inaccurate, unsupported or affected by greater judgement.

Perform risk-based procedures over selected source data, supporting evidence, methodologies, assumptions and calculations.

Assess whether sufficient appropriate evidence has been obtained to support an assurance conclusion and provide management observations where relevant.

Our procedures are risk-based and proportionate. We focus additional attention on areas involving materiality, estimation uncertainty, Scope 3 emissions, third-party information, manual processing and significant management judgement.

What standards do we use?

Our limited assurance engagements are performed using recognised assurance standards.

- ISAE 3410 is used for current assurance engagements over greenhouse gas statements.

- ISAE 3000 (Revised) provides the broader assurance framework for sustainability and other non-financial information.

- ISSA 5000 is the global sustainability assurance standard for the next phase of sustainability assurance. Our methodology is designed to help organisations prepare for its implementation.

ISSA 5000 applies to sustainability assurance engagements for periods beginning on or after 15 December 2026, with early application permitted. The UK Government is also developing a voluntary oversight regime for sustainability assurance practitioners, intended to build trust in the market and help companies identify qualified providers.

What you receive

Depending on the service selected, outputs may include:

An independent limited assurance statement suitable for agreed external reporting purposes
A structured findings and issue-resolution summary
Management observations and recommendations
Clearer evidence trails, methodologies and reporting documentation
Stronger data controls and ownership arrangements
A practical roadmap for future assurance readiness.

Why choose Acclaro

Independent & evidence-based

We provide independent limited assurance over agreed information, supported by a structured assessment of evidence, methodology, risk and reporting criteria.

Focused on the areas that matter most

Our work focuses on areas of higher potential misstatement, uncertainty and judgement, including Scope 3, third-party data, estimates, assumptions, manual processes and new reporting systems.

Broader than emissions data

We support assurance and readiness work across GHG emissions, sustainability metrics, climate disclosures, governance, risk management, targets and selected narrative reporting.

Practical for complex reporting requirements

We work with multi-site and multi-jurisdictional organisations, fragmented reporting systems, evolving carbon platforms and developing sustainability reporting processes.

Accountancy and assurance discipline

Our approach brings together sustainability subject-matter knowledge with the rigour expected from audit, financial reporting, governance and risk management.

Built for future assurance expectations

We help organisations strengthen evidence, controls and reporting discipline now, while preparing for ISSA 5000 and wider sustainability assurance expectations.