As a result of Brexit taking fully effect on January 1st 2021, there is a fair amount of confusion in particular among my British friends living here in France. In fact we had quite a lively discussion last weekend on the subject of EU v Schengen.
In the meantime I have made a little bit of research and can summarize the facts as follows:
The Schengen area started in 1985 when 5 countries (Germany, Belgium, France, Luxembourg and Netherland) decided to create between themselves a territory without internal borders. The treaty was signed in the town of Schengen (Luxembourg) hence the name of the treaty.
In the meantime other countries have signed the treaty with some not being in the EU (Switzerland*, Norway). Some EU countries are not part of Schengen (Ireland, Croatia, Romania, Bulgaria, Cyprus, (UK)).
Many agreements have been reached with countries around the world to give them access to a Schengen visa. The basic visa allows for a stay of 90 days. It should be applied to the Schengen country where the most time will be spent or in case of expected equal times spent in different countries, the application should made in the 1st country one intends to enter.
The Maastricht treaty, now superseded by the Amsterdam, Nice and Lisbon 2007, was signed in 1992 (7 years after Schengen) and founded the European Union. It renamed the European Economic Community into European Community.
The freedom of movement for workers in the European Union means that nationals of any member state of the European Union can take up an employment in another member state on the same conditions as the nationals of that particular member state*. It has little or nothing to do with internal borders as covered by the Schengen treaty. That will be a major part of the negotiations needed between the UK and the EU.
What sort of agreement will be reached with the UK for January 1st 2021 is anybody’s guess. It is however clear that non EU nationals, in the case UK nationals, with a residence permit in a EU country will not be affected.
* Which is why you can drive from France to Geneva without having to show your passport.
* The 1st freedom of movement treaty was the Treaty of Paris (1951) established the European Coal and Steel Community and establishing a right to free movement for workers in these industries.
It might be a bit clearer on the map
I do it my way 