Tegenaria atrica is a species common in continental Europe and the Republic of Ireland but on the British mainland it has long been regarded as a relatively rare import that has failed to establish. The recent discovery of this species in some numbers and over several years in Burnopfield, County Durham, represented the first-reported, self-sustaining population. We show here that the species is widespread across a large swathe of country comprising parts of north County Durham, Tyne and Wear, and south-east Northumberland — an area of some 710 km². Within a core range of approximately 400 km², the other species in the Tegenaria atrica group, T. saeva and T. gigantea, tend to be uncommon or absent. The distributions of these three closely related species raise questions regarding the origins of the T. atrica population, the effect of chance and priority in initial establishment, and the role of possible competitive interactions between them. Although determining ecological processes from present patterns of distribution is fraught with difficulties, it seems likely that T. atrica established and subsequently spread following a chance introduction, possibly in the Victorian era, to a region then devoid of close competitors. In the 1960s, when T. saeva and T. gigantea expanded their distributions northwards, priority effects may have protected the T. atrica population from invasion by these species, or at least slowed down the process. Future surveys are required to determine just how resistant the T. atrica population is to invasion and whether it, too, is expanding its range.