A lot has been said on this subject and no doubt it is a complete disaster in every way. To me one of the worst aspects of it will be the festering resentment created: within England, within Britain, and within Europe. There will be dislike and suspicion everywhere; ill feeling, anger, contempt. Even if it never comes about, though inefficiency or feet dragging, an awful lot of harm has already been done that cannot be rectified.
There really should be an explicit discipline called “political psychology” that deals with all aspects of the psyche that bear on politics (compare “economic psychology”). Political emotions would be a central area. Much of social science is still in thrall to behaviorism, but we need to recognize the full reality of the inner life in shaping behavior. In fact, most of political theory really is political psychology under another name. And the first law of political psychology is: People hate people with whom they disagree politically.