The United Kingdom’s National Referral Mechanism (NRM) is a framework for identifying potential victims of modern slavery (slavery, servitude, forced labour or human trafficking) and ensuring that they receive adequate care. This research explores differences in referrals and outcomes of potential modern slavery victims within the NRM on the basis of individual attributes, geography and first responder. Findings are based on exploratory analysis of data on 55,000 cases released by the Home Office in spring 2022 plus data from four Freedom of Information requests. Findings confirm that there are significant differences in rates of positive outcomes between native and immigrant groups, with native populations more likely to receive positive conclusive grounds (CG) decisions. Our key contribution is in identification of the role of the first responder in negatively influencing outcomes for victims of particular forms of exploitation. We suggest the differences in outcomes may be explained by the dual role played by first responders within the immigration system in identifying victims and implementing immigration control measures. We situate this finding within a broader critical migration literature on polymorphous borders pointing to the NRM as one mechanism through which bodies are differentially excluded from territorial access and associated rights or benefits.