Board Oversight Architecture and ESG Disclosure Quality: Complementarity and Substitution Between Audit and Sustainability Committees

This study examines how board committee architecture is associated with ESG disclosure quality in UK listed firms. Using an unbalanced panel of FTSE 350 firms from 2010–2023 and LSEG ESG disclosure scores, we test whether audit committee (AC) monitoring capacity, proxied by independence, financial expertise, meeting frequency and committee size, relates to ESG disclosure quality, and whether these relationships are conditioned by the presence of a sustainability committee (SC). Panel regressions with industry and year fixed effects and firm- level clustered standard errors show that each AC attribute is positively associated with ESG disclosure quality. SC presence is also positively associated with ESG disclosure quality, indicating that dedicated ESG governance structures are linked to more structured sustainability reporting. Interaction tests reveal heterogeneous conditioning effects: SC presence strengthens the associations for AC independence and meeting frequency but attenuates the associations for AC expertise and AC size. These findings show that board committees do not operate as uniformly additive governance mechanisms; rather, their contribution to ESG disclosure quality depends on how monitoring resources and ESG over sight responsibilities are configured across the board. The study contributes to the ESG governance literature by distinguishing complementary from substitutive relationships between audit and SCs. Robustness checks using pillar scores, firm fixed effects, lagged governance variables and alternative specifications yield consistent inferences.