Brexit: withdrawal of the United Kingdom and negotiation of its future relationship with the EU Mercedes Guinea Llorente Introduction: Brexit Acts I and II In this report we are going to deal once again this year with another chapter in the Brexit saga. This time we would like to carry out a double exercise: analysing the two different political processes that constitute Brexit. The first, which we might call Act I, took place from the referendum in 2016 to 31 January 2020, and was a con­stitutional political process considering that the aim of the negotiation was a change in the European polity in a direction contrary to the habitual one–a reduction in the number of member States. 1 In this analysis, we make 1 We have dealt with Act I of Brexit in several chapters of our reports on the state of the EU over the last few years. See Guinea Llorente, M.:“El brexit : las negociaciones de re­tirada del Reino Unido de la Unión Europea”, in: López Gar­rido, D.(ed.), Informe sobre el estado de la Unión Europea 2017. Relanzar Europa, Madrid, Fundación Alternativas-Friedrich Ebert-Stiftung, 2017, pp. 105-114; Guinea Llorente, M.: “Las negociaciones del brexit en la primavera de 2018: avances y perspectivas futuras”, in: López Garrido, D.(ed.), Informe sobre el estado de la Unión Europea 2018. Los Estados euro­peos ante las reformas de la Unión, Madrid, Fundación Alternati­vas-Friedrich-Ebert-Stiftung, 2018, pp. 55-67; Guinea Llor­ente, M.:“La incertidumbre del brexit: quo vadis Britannia?”, in: López Garrido, D.(dir.), Informe sobre el estado de la Unión Euro­pea 2019. El Parlamento Europeo ante unas elecciones trancendenta­les, Madrid, Fundación Alternativas-Friedrich-Ebert-Stiftung, 2019, pp. 123-134. an overall political assessment of the constitutional pro­cess of reduction. The mutation of Europe took place on 1 February 2020, the effective withdrawal date of the United Kingdom(UK). Although the process has not yet been completed, the European Union(EU) once again has 27 States. Its territory, population and wealth have been reduced and, as far as the EU is concerned, the United Kingdom has become a third-party State. This situation is not yet all that perceptible, as the legal effects have been delayed due to the transitional period lasting throughout 2020, which means EU law continues to ap­ply in the UK in an exceptional way. This year new negotiations have begun between the EU and the UK–Act II of Brexit–in which the legal frame­work to govern mutual relations from the end of the transitional period on 1 January 2021 is being discussed. These are substantially different negotiations–interna­tional ones with a third-party State–and their aim is to consider a possible association between the EU and the UK, covering economic, political and security matters. Our perspective will, as always, be that of the EU, par­ticularly taking into account the distinctive features of its political model, halfway between an international or­ganisation and a political system of its own. 87