Disclosure of multidisciplinary expertise in sustainability assurance: unpacking legitimacy and accountability for stakeholders in sustainability reports

Purpose This study aims to examine how multidisciplinary expertise is disclosed in sustainability assurance statements and how such disclosures shape stakeholder perceptions of accountability. Drawing on legitimacy theory, the analysis considers how assurance providers disclose team composition, assurance level and engagement scope to signal competence and trustworthiness. Design/methodology/approach Qualitative content analysis was conducted on sustainability assurance statements from 67 FTSE 100 companies for the reporting years 2022 and 2023. A conceptual framework is used to interpret how multidisciplinary expertise and assurance level (limited vs reasonable) relate to accountability and legitimacy outcomes. Findings Limited assurance remains dominant (94% of engagements). Although many firms disclose multidisciplinary expertise, 29.8% of these still report only limited assurance, indicating a continuing expectation gap around the credibility and decision-usefulness of sustainability information. Practical implications Assurance providers and standard setters may strengthen perceived accountability by increasing transparency about team expertise and encouraging greater adoption of reasonable assurance where sustainability disclosures inform stakeholder decision-making. Originality/value The study shows how disclosures of multidisciplinary expertise operate as part of legitimacy-seeking strategies within sustainability assurance. It offers insight into how assurance level and team composition are positioned within FTSE 100 sustainability reporting.