There has been much discussion around Article 50 of the Treaty of the European Union (TEU): what is says, what are the processes to bring it into play, when will it be operational and what does that mean. There are certain clear facts, some unknowns and lots of interesting legal theories emerging.
Article 50 TEU
1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.
2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining the consent of the European Parliament.
3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
4. For the purposes of paragraphs 2 and 3, the member of the European Council or of the Council representing the withdrawing Member State shall not participate in the discussions of the European Council or Council or in decisions concerning it. A qualified majority shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.
5. If a State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.
It is up to the Member State, having decided to withdraw, to act in accordance with its own "constitutional requirements". It will be up to the UK government to decide when the notification in para 2 is made. There is no set timeframe. While the EU may be keen for matters to proceed quickly, the timing rests with the UK.
What the "constitutional requirements" are is also not clear. The PM may merely need to exercise his prerogative power. However there are constitutional lawyers suggesting that Parliament, which means both Houses, should or must be consulted before notification is made. Some even suggest an Act of Parliament will be necessary, based on the argument that there is existing legislation within this area (the European Communities Act 1972), and therefore the prerogative power should not be exercised. A legal challenge in the courts may be pending.
There is also doubt as to whether the Scottish Parliament must be consulted under the Sewel Convention. While "International relations", including those with the EU, are reserved by Schedule 5 of the Scotland Act 1998, observing and implementing obligations under EU law are devolved. Arguably the devolved functions being exercised by the Scottish Parliament are being varied and therefore it should be consulted and consent sought. However, if the necessary Legislative Consent Motion was brought before it, and the Scottish Parliament did not consent, then the UK Government could probably still proceed legally, even with the amendment made to the Scotland Act 2016 putting the Sewel Convention, to some degree, on a statutory footing. Politically that would certainly be controversial and another first.
If there is Parliamentary involvement by Westminster or Holyrood, that has a practical impact on the Article 50 timetable. What is clear is that once the notification is made to the European Council there is a two year period allowed within which to carry out the negotiations for withdrawal. If the negotiations are not completed within two years then the UK would automatically cease to be a member on the expiry of that period unless it is extended with the unanimous agreement of the other Member States. The considered opinion is that this is a very short period within which to complete complex negotiations but might be enough to settle high level principles. Would that be sufficient to constitute a leaving agreement? In theory a withdrawal agreement could be completed in less than two years and that would be the relevant leaving date, but that seems practically unlikely.