[pmyteh]

According to the text of Article 50, a withdrawing state remains bound by the Treaties (and thus by EU law) until either (1) an exit agreement is made and enters into force; or (2) two years pass after Article 50 is invoked.

So the UK can't 'withdraw unilateral whenever it wants' without creating a giant legal problem as its erstwhile partners attempt to enforce its (still extant) obligations.

[gpderetta]

the UK is sovereign, so it certainly can. The other parties can of course impose sanctions (likely) or go to war (unlikely, hopefully).

[antientropic]

Sure, if the UK is willing to violate its treaty obligations, it can do whatever it wants. But the context of the discussion was the legal situation under Article 50.