Check this out:
The side link PDF: "23 Major Facts"
In particular, "#20 - The Discovery of America AD 562"
How the heck could bolide swarms burn ancient Britain "from sea to sea" without it being acknowledged by history?!
You do realize that as the Saxons fled whatever had happened further North and West, the Britons relocated to Brittany which needed to have every plant replanted (Merlin is credited with doing the vinyards, both here and at the headwaters of the Rhone Valley), and animals had to be brought in.
Here's the problem with history in NW Europe after the big event that destroyed civilization, there wasn't much civilization left and there was substantial depopulation of the region.
So, the loss of NW European civilization is KNOWN ~ it happened ~
St. Gildas describes building materials flying into the air! That's something more than a bunch of cowboys setting fire to the barn!
Today we know that the ancestors of just about everybody in the British Isles lived in the Western European refugia (Southern France and Northern Spain) in the ice age ~ and they just walked there as the ice moved out.
The particular celtic languages were brought about 700 BC from the Celtic evacuation of the Danube ~ so there is a minor volkswandering ~ but it wasn't a lot of people, just a leadership elite. They were technologically more advanced than the natives so they took over the place!~ still same ethnic group though.