Reply #6: No, the OP is about the flooding of the low-lying area between East Anglia

[muriel_volestrangler]

and, roughly, the northern Netherlands, called 'Doggerland' (now the Dogger Bank, underwater).

The formation of the English Channel, especially the Straits of Dover, which you link to, was earlier, and was caused by a freshwater lake bursting through the chalk formation that had linked Kent and France.

The OP is about the end of the last Ice Age - the Rhine (plus Thames) flowed into an estuary, and south through the Straits of Dover, but there was low-lying land the the north of that. This was gradually disappearing as sea levels rose from the retreat of the ice caps, but there was a sudden tsunami caused by landslides in Norway that flooded the coasts of the North Sea, including the north of Doggerland, and they think this was what finally broken the land bridge between Britain and the continent.