Any Semi-Realistic POD's For A Surviving Roman Empire Through Brtian

Just wondering for a possible timeline, but between Roman establishing permentat settlement and their withdraw, are their any POD's that one could take that would allow Rome continue in the British Islands/a little bit of the continent a la Byzantine even as the continental western one crumbles?
 
Well Britain went on pretty well until the Saxons and co. came and invaded. Maybe have a stronger economy and government remain in place along with a legion or similar force composed of Britons/Romans to protect them from invaders.

Typing from my phone right now so I can fit more in later
 
Somehow get the legions and Romans to stay in Britain. Maybe have Rome surprise screwed earlier and the people in Britain say "screw it, we're making this our Rome away from Home".
 
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