...soon after the end of the last Ice Age that prehistoric man wandered easily over the land bridge from the continent and started the colonisation of this land. According to this... http://news.bbc.co.uk/1/hi/sci/tech/5352430.stm
...the journey would have been tremendously difficult as there would have been an humungously big river, comprising the proto Rhine/Meuse/Thames flowing down what is now the English Channel. Click on the "open" tab to see the maps. They must have made it somehow as we're here aren't we!
Jim.