Building trust and readiness for sustainability assurance

This question sat at the heart of the formal launch of ICAEW’s Sustainability Assurance Certificate at Chartered Accountants’ Hall on 23 March 2026. The event saw practitioners and business leaders explore the role of sustainability assurance in supporting credible, decision-useful reporting and building confidence in sustainability-related information as it becomes increasingly integrated with mainstream corporate reporting.

Trust as the foundation

Opening the event, Ravi Abeywardana, ICAEW’s Director of Sustainability Reporting and Assurance, emphasised trust as the cornerstone of credible sustainability reporting and the critical role of assurance, ethics and professional judgement in helping to build it. He highlighted growing international momentum towards regulatory adoption of the International Sustainability Standards Board’s (ISSB’s) inaugural standards, IFRS S1 and IFRS S2, including the UK Government’s endorsement of UK Sustainability Reporting Standards (UK SRS) aligned to the ISSB.

He also pointed to the International Auditing and Assurance Standards Board’s (IAASB) International Standard on Sustainability Assurance 5000 (ISSA 5000), which will be effective in the UK from December 2026 through ISSA (UK) 5000. Importantly, he stressed that both the implementation of reporting and assurance need to develop in a proportionate, phased way, reflecting differing levels of organisational maturity and the operation of different assurance regimes that reflect this. This includes the UK’s voluntary sustainability assurance regime.

“Trust is the foundation of high-quality sustainability information. Once trust is lost, it’s incredibly difficult to get back,” Abeywardana said.

The launch of ICAEW’s Sustainability Assurance Certificate reflects the accountancy profession’s role in supporting trust in sustainability information, recognising that reporting is most effective when underpinned by robust assurance, strong ethical standards and practical capability building. It combines skills that already exist within the Audit and Assurance Faculty and wider ICAEW membership, with a new knowledge base.

Building on a solid audit and assurance base

ICAEW’s new course builds on the core skills that will be familiar to auditors of financial statements. Concepts such as risk, materiality, evidence and professional judgement remain central, providing strong scaffolding for practitioners moving into sustainability assurance. 

“The challenge for chartered accountants is not a lack of skills, but a knowledge gap,” Rosie Dunscombe, lead author of ICAEW’s new certificate and founder of Blue Crane Consulting, told the launch audience. She explained that the course is designed to support practitioners across the full assurance journey, from early readiness and limited assurance through to more mature engagements.

Developed for finance professionals, but acknowledging that many approaching this space will come from a grounding in financial statements audit, the e-learning course focuses on the practical application of assurance principles to sustainability information. It uses expert case studies, videos, knowledge checks and a final assessment to bring sustainability assurance to life and reinforce key assurance and ethical considerations.

From ambition to implementation

Alex Russell, Audit and Assurance Director at ICAEW, moderated an insightful panel discussion, which brought together perspectives from across the sustainability reporting and assurance ecosystem, including Dunscombe, Michelle Olckers, Partner, Audit & Assurance, Forvis Mazars, Pauline Irwin, Director, Global Quality Assurance, PwC, Alison Dundjerovic, Director, National Audit & Assurance, Deloitte, and Andrew Stormer, Head of Sustainability Reporting, Standard Chartered. 

There was strong consensus that sustainability assurance is not one size fits all, and that progress should be based on clear scoping and steady, well-judged decisions grounded in assurance expertise, professional judgement and common sense.

Sharing a preparer’s perspective, Stormer highlighted the importance of organisations being clear on what information they want to get assured, with good governance in place where judgements and key decisions are well understood and documented. 

The panel discussion also highlighted the central role of professional skills, ethics and multidisciplinary working in delivering credible sustainability assurance. With sustainability-related financial information becoming increasingly mainstream due to regulatory requirements, and therefore comparable with traditional financial information, the core principles of high-quality assurance remain unchanged. This makes existing statutory audit experience a strong and relevant foundation on which to build sustainability assurance capability. 

Preparing the profession

Closing the event, Abeywardana returned to the central theme of trust. Sustainability reporting and assurance, he noted, are on a journey. The training and experience of ICAEW members – which includes professional scepticism, understanding systems and controls, exercising judgement and ensuring information is decision‑useful –  offer a strong foundation that can help build trust and support the evolution of sustainability reporting and assurance.  

Now live and open for enrolment, the ICAEW Sustainability Assurance Certificate provides a practical pathway for members and firms to build capability and respond to growing demand for sustainability assurance.

For ICAEW members, the message is clear: sustainability assurance presents both challenge and opportunity. With the right skills, standards and professional judgement, chartered accountants are well placed to help build trust where it matters most.

Ten key takeaways for assurance practitioners

1. Trust sits at the heart of sustainability assurance 
   As sustainability information increasingly informs strategic and investment decisions, assurance plays a critical role in building, and maintaining, trust through robust standards, ethical behaviour and professional judgement.
2. Sustainability assurance builds on what practitioners already know
   Risk assessment, materiality, evidence, professional scepticism and judgement remain the backbone of high-quality assurance on sustainability-related information. While sustainability assurance introduces new subject matter and data challenges, practitioners are not starting from scratch – the core assurance model still applies.
3. ISSA 5000 provides a much-needed global baseline
   The introduction of ISSA 5000, and its UK equivalent ISSA (UK) 5000, marks an important step towards consistent, credible sustainability assurance. When combined with the Global Ethics Sustainability Standards from the International Ethics Standards Board for Accountants (IESBA), the global framework reinforces both how assurance is performed and the ethical mindset required to protect independence, objectivity and public trust.
4. Ethics and independence are non negotiable
   Strong ethical standards underpin credible sustainability assurance. Practitioners must remain alert to independence threats, greenwashing risks and pressure from management, particularly in fast-developing or highly judgemental reporting areas.
5. Proportionality and phasing are essential to progress
   There is no one-size-fits-all model for sustainability assurance. Effective engagements adopt proportionate, phased approaches that reflect organisational maturity, reporting scope and the needs of intended users, often starting with limited assurance and evolving over time.
6. Readiness matters as much as assurance execution
   High-quality assurance depends on preparer readiness, robust governance, clear roles and responsibilities, suitable criteria and reliable data processes. Where these preconditions are weak, practitioners play an important role in challenging engagement acceptance and avoiding assurance that risks undermining trust.
7. Materiality judgements require both rigour and common sense
   Sustainability materiality is often more complex and involves navigating multiple lenses: financial and impact materiality. Applying a stand-back, common-sense approach, focused on what truly matters to intended users, is critical alongside professional judgement, and remaining alert to aggregation risk, particularly for qualitative disclosures.
8. Connectivity with the financial statements cannot be ignored
   Sustainability information and financial reporting are increasingly interconnected. Climate and sustainability-related risks and opportunities can have financial impacts that cut across both reporting streams, reinforcing the need for close coordination between sustainability assurance and financial audit teams.
9. Multidisciplinary working strengthens assurance quality
   While assurance practitioners remain responsible for the conclusion, sustainability engagements often require input from subject matter experts. The challenge is not whether to involve experts, but how to integrate their work while maintaining independence, objectivity and overall assurance quality.
10. Building capability is both a challenge and an opportunity
    Sustainability assurance highlights a knowledge gap rather than a skills gap for many chartered accountants. Continuous learning, supported by structured training and practical experience, will be essential as standards evolve and demand for credible sustainability assurance continues to grow.