Stakeholder influences have led to rising pressures on the architecture, engineering, and construction (AEC) sectors to support the delivery of the sustainable development agenda. Responsible and ethical procurement has emerged as a tool for positive organisational processes; however, engagement remains limited among small and medium enterprises (SMEs). BES6001 is a point-based UK framework standard for responsibly sourced construction materials, which encompasses social, economic, and environmental dimensions of supply chain management. Despite increased expectations on organisations to achieve certification for their materials, SME achievement of certification remains limited. Mirroring approaches used in an earlier study (Upstill-Goddard et al., Proc ICE: Eng Sustain 168(2): 71–81, 2015), this study aims to investigate relationships between individual clause scores and levels of attainment in SMEs versus major industry players. Using assessment score data from certification information obtained (including company size, attainment level, and product sector), statistical procedures (Spearman’s Rank and Cronbach’s Alpha) were used to ascertain that a systematic imbalance exists between SMEs and larger organisations in obtaining accreditation. Therefore, the study surmised that SMEs needs to adopt a more strategic approach to responsible sourcing, and they need investment in the larger clauses to offset more limited funding. Based on these findings, the study sets out a suite of recommendations to enhance the outcomes for SMEs, which include: (i) SMEs need to be more strategic and prioritise clauses where maximum differential can be achieved (such as resource use and transport impacts); (ii) SMEs need to engage their businesses with like-minded suppliers branding similar environmental certifications, in order to meet the criteria required to gain the highest marks in the clauses that provide the highest levels of differentiation; and (iii) where possible, SMEs should seek to prioritise investment in environmental management systems (such as BS8555 or ISO14001) to increase their scores.