The SEA's signing grew from the discontent among European Community members in the 1980s about the de facto lack of free trade among them. Leaders from business and politics wanted to harmonise laws among countries and resolve policy discrepancies. The Treaty was drafted with the aim of implementing parts of the Dooge report on institutional reform of the Community and the European Commission's white paper on reforming the Common Market. The resultant treaty aimed to create a "Single Market" in the Community by 1992, and as a means of achieving this adopted a more collaborative legislative process, later known as the cooperation procedure, which gave the European Parliament a real say in legislating for the first time and introduced more majority voting in the Council of Ministers. Under the procedure the Council could, with the support of Parliament and acting on a proposal by the Commission, adopt a legislative proposal by a qualified majority, but the Council could also overrule a rejection of a proposed law by the Parliament by adopting a proposal unanimously.
Signing and ratification
A political agreement was reached at the European Council held in Luxembourg on 3 December 1985 when foreign ministers finalised the text. Denmark and Italy raised concerns over constitutional validity. Nine countries, Belgium, the Federal Republic of Germany, France, Ireland, Luxembourg, the Netherlands, Portugal, Spain, and the United Kingdom, signed the Single European Act at Luxembourg on 17 February 1986. That date was originally intended as display of unity within the Community regarding the SEA, but this failed. The Danish parliament rejected the Single European Act in January 1986 after an opposition motion calling for the then unsigned document to be renegotiated was passed by 80 votes to 75. The Danish opposition opposed the treaty because they said it would increase the powers of the European Parliament. The Danish government, who supported the treaty, decided to hold a national, non-binding referendum on the issue to overcome the treaty's rejection by the Danish parliament. This referendum was duly held on 27 February 1986 and approved by the Danish people by 56.2% voting in favour to 43.8% against on a turnout of 75.4%. The Italian government delayed in signing for the opposite concern: that, in their opinion, it would not give the European Parliament enough power. Together with Greece who had also delayed in signing, Denmark and Italy signed the Single European Act at The Hague on 28 February 1986. It had been originally intended to have the SEA ratified by the end of 1986 so that it would come into force on 1 January 1987 and 11 of the then 12 member states of the EEC had ratified the treaty by that date. The deadline failed to be achieved when the Irish government were restrained from ratifying the SEA pending court proceedings. In the court caseCrotty v. An Taoiseach, the Irish Supreme Court ruled that the Irish Constitution would have to be amended before the state could ratify the treaty, something that can only be done by referendum. Such a referendum was ultimately held on 26 May 1987 when the proposal was approved by Irish voters, who voted by 69.9% in favour to 30.1% against, on a turnout of 44.1%. Ireland formally ratified the Single European Act in June 1987, allowing the treaty to come into force on 1 July.
At the end of January 2020, the UK left the EU and so withdrew from this Treaty.