At the end of the last ice age, Britain formed the northwest corner of an icy continent. Warming climate exposed a vast continental shelf for humans to inhabit. Further warming and rising seas gradually flooded low-lying lands. Some 8,200 years ago, a catastrophic release of water from a North American glacial lake and a tsunami from a submarine landslide off Norway inundated whatever remained of Doggerland.
Britain, as it looked in 5,500 BC
Hypothetical Landscape with extensive coast and estuaries Earlier Holocene