<p>Technology can augment the interaction between patients and the healthcare system, but its adoption can vary widely across patients due to their personal circumstances or supply-side features. We formulated this study to answer the following variable importance question: which patient, workforce and organisational characteristics are the most important at driving adoption of the online access route to primary care among the population in London? We examined the importance of each candidate treatment variable in separate analyses by contrasting online access adoption under low and high-adoption levels of each candidate variable. We used practice-level data from the population in North West London between 2018 and 2021 and employed the cross-validated targeted minimum loss-based Estimation to obtain variable importance estimates. We found that the top two drivers of online access adoption are the socioeconomic deprivation of the registered patient population and digital maturity of the practice, followed by quality of care measured by an inspection rating, helpfulness of receptionists, internet connectivity at the residential area of patients, practice’s training status and patients’ comorbidity profile. Our results highlight the potential areas of focus when designing interventions to facilitate online access adoption in primary care across the population. These areas of focus include mitigating the impact of patients’ socioeconomic deprivation on using digital technology and improving organisations’ digital maturity by investing in their infrastructure and workforce’s digital capability.</p>