This article examines the intersection of religious faith and the ‘fight against modern slavery’ in the UK, as yet unexplored in sociological literature. Analysis of faith based organisations’ (FBOs) activities in this area challenges understandings of a postsecular rapprochement between faith and secular actors - where postsecular is used by some scholars to refer to the re-emergence of faith in the public sphere, and where we understand rapprochement to mean the placing of equal value on faith-based and secular worldviews. Our research reveals that FBOs in the anti-trafficking/modern slavery third sector operate on a ‘dual register’, secularising as they professionalise their public face, while retaining religious distinctiveness when engaging with co-religionists. We argue that, rather than evidence of a genuine two way postsecular rapprochement, it seems that FBOs in this sector are prioritising secular modalities, meaning the learning process is one-sided rather than complementary.