From Barnier's crime speech- it sums up the govt's #Brexit problem. UK says let’s have bespoke arrangements which will benefit both of us (and satisfy our red lines). EU says you don’t understand: we are a legal and institutional order and we can’t. Then repeat ad nauseam. 
The UK constitiution is practically made of fudge: based on gradual evolution and compromise. For many British politicians this is their reflex: where there is a will, there's a way. This usually virtuous position is not helping the govt much in understanding their opponents.
The intellectual case for post-Brexit rested on this idea: we are powerful enough that we can cut a bespoke deal which would escape the strictures of their legal order. We'll know whether that was right at the end of all this but on balance of negotiations so far it looks flawed.
