Estimates are assembled for England, Wales, Scotland, and Ireland, and for Britain and Ireland as a whole, of the numbers of religious houses, regular clergy, parishes, towns of more than 2,000 inhabitants, and townspeople, and the value of dutiable exports and volume of currency at the watershed date of c.1290. Absolute and relative levels of economic development are then compared. A range of possible population estimates are considered and corresponding set of per capita estimates thereby derived. The results highlight significant differences in the pattern of economic development between and within these four countries.