Comparison of a rigorously selected group of calibrated carbon-14 dates suggests that the overlap of Mesolithic and Neolithic technologies lasted at least 300 years in Britain and 800 in Ireland (at 1sigma). Reasons for this are examined and a more flexible approach to the customary Mesolithic/Neolithic divide called for. Some cultivation by indigenous hunter-gatherers does seem to be indicated, although regular food production (especially in Ireland) was probably introduced by immigrants from Europe.