Regulatory regimes can influence the structures of the industries being regulated and the residential development industry is no exception. Such industrial effects are often the direct goals of regulation policy but in the case of housebuilding it is a generally unrecognised by-product of land-use planning policies. The UK has both one of the most concentrated housebuilding industries in the world and one of the most restrictive land-use planning regimes. This paper examines the degree of concentration in the UK housebuilding industry, nationally and regionally, and examines various potential benefits of scale in housebuilding. Empirical evidence suggests many scale economies seem to be exhausted at relatively small firm sizes. However, this is not the case for land purchase and planning negotiation. Greater size does not seem to provide firms with higher profit margins, even so the resultant industrial structure may have implications for market efficiency and the elasticity of housing supply.