On 29 March 2017, UK Prime Minister Theresa May lodged with the EU Council a notification under Article 50(2) EU Treaty, i.e. the UK's formal notification of its intention to withdraw from the EU.
This notification triggers a two-year period for negotiations between the UK and the rest of the EU which should culminate in a withdrawal agreement.
Failing such an agreement, the UK will, in principle, leave the EU by operation of law after the two-year period (“hard Brexit”).
As this is the first time in the history of the EU that the article 50 exit procedure has been triggered, there is no clear and tested roadmap.
Depending on whether there is to be a hard Brexit or a negotiated Brexit, the legal landscape will be quite different after March 2019.