At the end of the Early Pleistocene (1 million to 800,000 years ago) Britain was permanently linked to mainland Europe, giving easy access for humans, who left their flint tools behind at Happisburgh. The river drainage was totally different. The Thames flowed through Suffolk and Norfolk into the North Sea, while an extinct river, the Bytham, flowed from the Midlands across East Anglia. These rivers deposited sands, gravels and estuarine muds that form the Cromer Forest-bed.
early Middle Pleistocene
Over the following 300,000 years the rivers continued to flow across East Anglia with the Thames migrating further to the south. Through this period there were marked oscillations in climate from cold glacial phases through to warmer periods or interglacials.
Humans continued to make occasional visits during the warmer periods for example at Pakefield in Suffolk 700,000 years ago or at Boxgrove in Sussex, 500,000 years ago.
About 450,000 years ago a large ice-sheet covered most of Britain destroying the Bytham River and forcing the Thames south into its current valley through London. As the ice melted thick glacial deposits of sands and clays were left behind and in Norfolk and Suffolk form many of the cliffs that we see today. The meltwaters formed a lake in the North Sea Basin and as the water rose it forced a passage through the Chalk to the south forming the Strait of Dover. As sea levels rose Britain became an island.