This article uses Kingdon’s multiple streams approach to analyse the implementation gap between anti-slavery legislation and front-line practice, with particular reference to emerging challenges in the implementation of the UK’s 2015 Modern Slavery Act. The multiple streams approach suggests that policy change and implementation depends on an active coupling of problems, politics and policy, often by proactive ‘policy entrepreneurs’ drawing upon supportive policy communities. While this conjunction can be observed in the framing of the UK’s anti-slavery policy at a national level, document review and survey evidence suggests a failure to consistently replicate the same elements at a local level. It is suggested that this has resulted in differentiated engagement with anti-slavery policy from crucial local partner organizations, including UK local authorities and the voluntary sector. While in some cases local ‘focusing’ events, politics and policy entrepreneurs have helped to galvanize partnership action, in many localities there is a lack of coordination, resource and impetus. The article makes recommendations to strengthen local implementation, including attention to reframing the ‘problem’ of modern slavery, to ensure that it has resonance for local stakeholders, including local political leaders. It is also important for government to recognize competing demands on service providers, and address contradictions that lead to tensions at the front line, particularly between victim care and immigration enforcement. Future policies could also more proactively support local policy networks and communities engaged in anti-slavery activity, embracing different conceptions of the policy challenge beyond a criminal justice perspective. These findings have relevance not only for the UK but also for other nations considering how to embed anti-slavery policy into local practice.