During the earliest periods of human occupation, the geography of Britain differed considerably from that of today. Britain was not an island but a peninsula of the north-west European continent. 900,000 years ago there was no English Channel, but a precursor of the river Thames flowed, far to the north of its present valley, reaching the North Sea at Happisburgh. This land bridge was the point of entry into Britain for migrating animals, including humans. Source: Ancient Human Occupation of Britain project http://www.ahobproject.org/