Real-life London is already known for its heavy use of surveillance technology. Watch Dogs Legion's post-Brexit London is a whole new level of tech dystopia. Drones are now heavily integrated into society, some of which are basically flying cops, equipped with weapons and scanning for troublemakers at all times. A new private security company, Albion, has gained influence across the city. Blume, the evil tech super company from the last two games, still appears to be pulling the strings behind the scenes.
It turns out that, while Brexit might have informed some of the story or decisions Ubisoft made about the game, the choice of location was made before Brexit was all we could talk about. Before Brexit, things were already a little bleak. Surveillance has been a concern seemingly forever.