24 Feb 2017 17:00:
Britain signed the Treaty of Maastricht and the Treaty of Lisbon which was later ratified by the British Parliaments. I accept Brexit was a vote to withdraw from these treaties. That is no reason for the EU to change anything. Britain will be gone and the EU will go from strength to strength holding fast to it's political principles. If it does not it's finished.
Free movement of persons
Freedom of movement and residence for persons in the EU is the cornerstone of Union citizenship, which was established by the Treaty of Maastricht in 1992. Its practical implementation in EU law, however, has not been straightforward. It first involved the gradual phasing-out of internal borders under the Schengen agreements, initially in just a handful of Member States. Today, the provisions governing the free movement of persons are laid down in Directive 2004/38/EC on the right of EU citizens and their family members to move and reside freely within the territory of the Member States, although substantial implementation obstacles persist.
Article 3(2) of the Treaty on European Union (TEU); Article 21 of the Treaty on the Functioning of the European Union (TFEU); Titles IV and V TFEU.
The concept of the free movement of persons has changed in meaning since its inception. The first provisions on the subject, in the 1957 Treaty establishing the European Economic Community (1.1.1, 3.1.3 and 3.1.4), covered the free movement of workers and freedom of establishment, and thus individuals as employees or service providers. The Treaty of Maastricht introduced the notion of EU citizenship to be enjoyed automatically by every national of a Member State. It is this EU citizenship that underpins the right of persons to move and reside freely within the territory of the Member States. The Lisbon Treaty confirmed this right, which is also included in the general provisions on the Area of Freedom, Security and Justice.
A.The Schengen area
The key milestone in establishing an internal market with free movement of persons was the conclusion of the two Schengen agreements, i.e. the Agreement proper of 14 June 1985, and the Convention implementing the Schengen Agreement, which was signed on 19 June 1990 and entered into force on 26 March 1995. Initially, the Schengen implementing Convention (signed only by Belgium, France, Germany, Luxembourg and the Netherlands) was based on intergovernmental cooperation in the field of justice and home affairs. A protocol to the Amsterdam Treaty provided for the transfer of the ‘Schengen acquis’ (5.12.4) into the Treaties. Today, under the Lisbon Treaty, it is subject to parliamentary and judicial scrutiny. As most Schengen rules are now part of the EU acquis, it has no longer been possible, since the EU enlargement of 1 May 2004, for accession countries to ‘opt out’ (Article 7 of the Schengen Protocol).
EU fact sheet on the European Union.