One way of looking at it is that Parliament has a mandate to do a completely insane thing but no formal instruction as to how to accomplish that completely insane thing. A casual observer of the negotiations would conclude that all parties are attempting to minimize the insanity to the best of their ideology but that competing ideologies have hampered the progress towards complete insanity. Effectively, Britain's inability to collectively agree on partial insanity will permanently forestall all attempts at complete insanity.
The referendum feels fundamentally flawed in that it asked "Do you want to leave of do you want to remain" with there only being a plan for one of the things. And the other being a completely insane thing, with no plan and impossible to deliver as advertised.