Brexit and the Irish border in the context of "European single market"

The European single market, also known as the European internal market or the European common market, is the single market comprising mainly the 27 member states of the European Union (EU). With certain exceptions, it also comprises Iceland, Liechtenstein, Norway (through the Agreement on the European Economic Area), and Switzerland (through sectoral treaties). The single market seeks to guarantee the free movement of goods, capital, services, and people, known collectively as the four freedoms of the European Union. This is achieved through common rules and standards that all participating states are legally committed to follow.

Any potential EU accession candidates are required to make association agreements with the EU during the negotiation, which must be implemented prior to accession. In addition, through three individual agreements on a Deep and Comprehensive Free Trade Area (DCFTA) with the EU, Georgia, Moldova, and Ukraine have also been granted limited access to the single market in selected sectors. Turkey has access to the free movement of some goods via its membership in the European Union–Turkey Customs Union. The United Kingdom left the European single market on 31 December 2020. An agreement was reached between the UK Government and European Commission to align Northern Ireland on rules for goods with the European single market, to maintain an open border on the island of Ireland.

The Irish Sea border is an informal term for the trade border between Northern Ireland and Great Britain. It was specified by the Ireland/Northern Ireland Protocol of the Brexit withdrawal agreement (February 2020), was refined by the Joint Committee in December 2020, and came into effect on 1 January 2021 following the end of the Brexit transition period. As a result of the Agreement, Northern Ireland remains aligned to the European Single Market in a limited way for goods, whilst remaining part of the United Kingdom customs territory and the UK internal market. Its effect is that the need for customs checks on the Irish border has been avoided, and a hard border has not been re-established.

This Irish Sea border was the option taken by Prime Minister Johnson in October 2019 to break the impasse of the "Brexit Trilemma" (of three competing objectives: no hard border on the island; no Irish Sea border; and no British participation in the European Single Market and the European Union Customs Union: it is not possible to have all three.)