"A catastrophic megaflood separated Britain from France hundreds of thousands of years ago, changing the course of British history."

Utter bollocks. Even if you make a cursory glance at the internet you can find that gradually rising sea levels had reduced "Doggerland" to a series of low lying islands which were then consumed by the sea.

A Tsunami caused by a massive landslide off the coast of Norway MAY had led to a temporary rise in sea levels.

@Although Doggerland was permanently submerged through a gradual rise in sea level, it has been hypothesized that coastal areas of both Britain and mainland Europe, extending over areas which are now submerged, would have been temporarily inundated by a tsunami triggered by the Storegga Slide. This event would have had a catastrophic impact on the Mesolithic population at the time.@ (Wiki)