A recent hypothesis postulates that much of the remaining coastal land was flooded by a megatsunami around 6200 BCE, caused by a submarine landslide off the coast of Norway known as the Storegga Slide.
Another view speculates that the Storegga tsunami devastated Doggerland but then ebbed back into the sea, with the later bursting of Lake Agassiz (in North America) releasing so much fresh water that sea levels over about two years rose to flood much of Doggerland and make Britain an island [REF].