Hold on, that's a snapshot of the Last Glaical maximum (Devensian) from about 28kya. You could just as easily selected the UK's actual glacial spatial maximum from earlier in the Pleistocene (Anglian) glaciation (478-424kya) when the ice front stretched from the the Isles of Scilly and the Western Approaches,across to South East England where it diverted the River Thames from its old course through the Vale of St Albans south to its present position.
So, I'm not quite sure this glacial determination has much credibility, tbh!
View attachment 238789
Have you Northern types considered the Danelaw demarcation yet?
View attachment 238790