Purpose: The United Kingdom (UK) construction sector is transforming with increasing confidence in offsite construction (OSC) solutions following its accrued benefits. To sustain this momentum, exploring viable strategies to promote successful OSC implementation is a top priority. This paper aims to identify and establish interrelationships and logical dependencies of critical success factors (CSFs) for implementing OSC on building projects in the UK. Design/methodology/approach: This study utilised a qualitative research approach. Following a critical review of extant literature, brainstorming and focus group sessions were carried out with OSC experts in the UK construction industry to identify and contextualise CSFs for OSC implementation. Interpretive structural modelling (ISM) and matrix impact cross-reference multiplication applied to a classification (MICMAC) were used to analyse and model the interrelationships between the contextualised CSFs. Findings: The study identified eighteen CSFs for implementing OSC on projects in the UK positioned on seven hierarchical levels and clustered into dependent, linkage and independent factors. The top five CSFs established were client commitment, top management support, adequate OSC knowledge and experience, flexible leadership and flexible business models. These were located at the base of the ISM model, possessing the highest driving powers in facilitating the successful implementation of OSC on projects. Originality/value: This study established a hierarchical interrelationship and the importance of the CSFs influencing the successful implementation of OSC. This would assist OSC clients and project teams in identifying and prioritising particular areas for strategic actions, which offer advantages in pursuing successful OSC project outcomes in the UK. Previous research on OSC implementation in the UK had not examined CSFs' interrelationships.