AHC: Anglo-French mutual invasions, wars, alliances, personal unions, or significant general politic

  I don't know if either group had the resources during most of this period, especially not the Anglo-Saxons as for most of this time they were busy securing what became England, fighting internally or against local threats - Scots, Welsh/Britons - then the assorted Vikings.

  There was something I did read a long while ago that in the early period the Franks did defeat an attempted Saxon landing/settlement on the mainland which IIRC was somewhere in the Bay of Biscay and it did suggest that less Saxons might have made it to Britain if they had been successful and more people had gone in that direction.  Think but could be wrong that this was mainly a force from Saxony rather than from Saxon settlements in England.  Looking at the wiki entry for Saxons it mentions:

  Think this was the case I was thinking of.  Its possible that if Eadwacer had been more successful then a Saxon kingdom was established in NW France instead or possibly as well as southern England.  Which is likely if it lasts to complicate matters and 'England' as we know it may be more dominated by Angle and Jutish culture although how different that would have made it I don't know.  If such a kingdom had succeeded and including in its territory Brittany then that rules out that location for Britons seeking to leave southern England so where they would go - or with less Saxons in England possibly Wales is a significantly larger state?

  That's as near as I can think of for a conflict or tension that matches your suggestion.