Following the Japanese earthquake and tsunami of March 2011, and the impact on nuclear power facilities, coastal communities around the world are re-evaluating the potential risk from tsunami hazard. Although the coastline of Britain has experienced few large tsunami some have occurred, such as tsunami generated by the prehistoric Storegga submarine slide and the 1755 Lisbon earthquake. Also, in southwest Britain, a flood in 1607 inundated lowlands along 540km of the Bristol Channel and the Severn Estuary coast, killing approximately 2000 people and causing much damage. The source of the 1607 flood is disputed, being caused either by a storm surge or tsunami. Evidence for two earthquakes in 1607 is presented here for the first time, suggesting this was a seismically active period. This has relevance for future planning of nuclear power facilities in the Bristol Channel, which is currently the location of the Hinkley, Oldbury, and (now decommissioned) Berkeley nuclear power stations.