Three species/area regressions are given for the British land mollusc fauna. As expected, the slopes of these regressions are shallow; Britain is biogeographically uniform. There is, however, a latitudinal gradient in species richness that influences the slopes. When this is quantified, and area and latitude allowed for, islands around the British mainland do not have impoverished faunas relative to the mainland. This finding runs counter to theoretical expectations, and to findings on offshore island molluscs elsewhere. The regressions based on relatively large areas appear to hold good down to tiny scales (1 m² or less); there is no consistent steepening at these scales. Quantification of such relationships at a wide range of scales will make broader European and global comparisons more rigorous.