Donald Tusk addressed the European Policy Centre on 13th October on several issues, one of which was Brexit, but in a wider context of the current concerns about the Ukraine and its effect upon the Eastern side of the Union. Let us not forget that the architect of the issues gluing the nascent Germany post the Conference of Vienna, including the Franco-Prussian War as a bonding agent, was Otto von Bismark, a Prussian

The link to his speech, but more importantly to his answers to the first and last questions will be given at the end of this short briefing. It is clear that the audience at the European Policy Centre was placing questions from a platform adverse to Brexit

It is essential to bear in mind that he is the President of the European Council, that is the Member States in council. He is therefore not speaking on behalf of the EU Executive - the Commission or associated advisory bodies, neither is he speaking on behalf of the European Parliament.

Article 50 lays down the principle for the process of withdrawal as lying in the communication of a Member State's Decision which is to be taken according to its internal constitution. That measure is notified to the Council, not to any other organ of the EU, nor in fact to the EU itself.

That is where the subtlety lies. Competences retained and conferred.

The decision to withdraw necessarily is a retained competence of a Member State. It is not governed exclusively if at all by any Union law. It is governed by the basic principles of Treaty law in international law. The type of Decision to withdraw from a Treaty is also not a final binding one in international law, as no State can be held to it. Switzerland withdrew its application to join the EU, although that may no be a useful analogy here.

At this level, although it has developed internally to adolescence from a foetal state, the European Union is merely composed of the competences conferred upon it by the Member States, One of the rôles of the Council is to supervise the exercise of those conferred competences. Where a given competence is not and has not been conferred upon the Union in International Law, then that competence remains with the Member States. The process of withdrawal for the Treaties , by definition a reserved competence, is therefore not subject to the EU Treaties as a matter of their internal operation, although a limited procedure is laid down at article 50 et seq. That TEU procedure is not a complete legal definition of the process or of competence at the International Law level relating to Treaty withdrawals. No Member State in its right mind would have signed up to any further limitation of its competence to withdraw.

An elegant review of the legal position on Kompetenz-Kompetenz and the other issues raised by Aurel Sari, Lecturer in International Law at Exeter University can be found  here.

The Court of Justice of the European Union has acknowledged that the EU must respect international law in the exercise of its powers (Case C-286/90, Poulsen and Diva, para. 9). Pursuant to Article 68 Vienna Convention on the Law of Treaties, a notification to withdraw from a treaty in accordance with its provisions may be revoked 'at any time' before the notification takes effect.

That puts the United Kingdom in a very strong negotiating position before the end of the Two Year period in that it can withdraw its notice up to the last minute and then renotify it ......

Suffice it to say, that the fact that the Decision is to be notified to the Member States in Council as States within the organisation of an international body, does not render the decision as such subject to an internal form of irrevocability. The EU only has the competences conferred upon it by the Member States, to the extent that any exercise of a competence has in fact been regulated by the Treaty, which may be the case here, then the Member State remains as free to revoke its decision as it would be in any other Treaty situation. See the references to such withdrawals from other Treaties in Aurel Sari's short commentary.

In other words, in this instance we may be" on the cusp" where general international law of Treaty interpretation, whether as codified in the Vienna Convention on the Interpretation of Treaties or not, meets the EU Treaty itself. It is well known that the CJEU does not consider itself to be bound by the Vienna Convention within the actual Treaty itself, however that position may well not be applicable on this "cusp", as a Member State could argue forcibly that it has only given certain competences to the European Union, not all.

There have been similar issues raised at the level of the German Constitutional Court in the Lisbon Case

SO: when Mr Tusk replies that he has not come across one head of State in Europe that wants Brexit, he is inferring that there could be support at that level of the Union, the highest, for a unilateral withdrawal of the article 50 notice once it is lodged. That is what he infers. That is not their being "nice", albeit that the older meaning of "nice" is apt, it is their being expedient as each does not wish to compromise their reserved competences in relation to the Union

He did not state although this may be inferred that it goes to each Member State's retained competence, as that inevitably would have weakened the Council's general negotiating position by an immediate internal division each State reckoninjg its own position in the future in relation to its retained competences and as to their extent.

When he then says that there is no legal or formal obstacle to allowing a withdrawal of the article 50 Decision, then there is no legal or formal reason why it cannot.

If everything or at least what he is saying is negotiable, then it is.

His neat speech can be found at this link his specific reply to the third question is transcribed here here