[naturalman1975]

It's hardly something I am an expert in - but this may explain things: Article 50 TEU: Withdrawal of a Member State from the EU

I'm told it does by people who are apparently experts. Short version as I understand it - Article 50 is fairly unambiguous (Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.) whereas whether withdrawal under clausula rebus sic stantibus is highly debatable for two reasons - references to the EU as inherently permanent in what is now Article 53, and the fact that the UK would find it hard to argue that the possibility of 'changed circumstances' had not been contemplated, given the debates of the 1970s (where British politicians expressly stated that they worried the treaty would be broadened) - under the Vienna conventions, clausula rebus sic stantibus does not apply if the changes were contemplated and so should have been taken into account when the treaty was signed.

[Olog-hai]

Read the rest of Article 50, especially paragraphs 2 and 4. The last thing the EU respects is a member state’s “own constitutional requirements”, and the reaction of the EU at large to the referendum speaks volumes. Invoking rebus sic stantibus does not give any advantage to the EU but subjects it to the laws of treaties, which they have violated multiple times; it also means that nothing within the treaties can be binding on the UK once invoked, whereas Article 50 binds the UK.