Adapting the current management of marine resources to align with an ecosystem-based approach is becoming increasingly common. Understanding the communities within an area—their species and distribution—is crucial to managing marine activities whilst maintaining ecological function. We performed a broad-scale community analysis of the demersal assemblages of the western English Channel and Celtic Sea. The diversity of the study area was investigated through K -means cluster analysis, indicator species analysis, diversity indices and discussion in relation to relevant environmental variables. The demersal species studied formed 7 distinct demersal assemblages, broadly aligned with environmental variables such as natural disturbance and substrate. Several assemblages were defined by notable characterising species, including Norway lobster Nephrops norvegicus in the Celtic Sea, queen scallop Aequipecten opercularis in the central western English Channel and boarfish Capros aper off the coast of the Cornish peninsula and the Isles of Scilly. The area of the central English Channel dominated by queen scallop had lower diversity relative to neighbouring demersal assemblages. This study provides the most spatially comprehensive delineation of demersal assemblage structure for this region, and is an example of the spatial analyses needed to inform future biodiversity monitoring and marine spatial planning, which are both key aspects of an ecosystem-based approach for the management of human activities in marine waters.