The Irish government supported this proposal.  It was strongly rejected by the Democratic Unionist Party as a weakening of Northern Ireland`s place in the UK and is seen as the main reason why Theresa May`s withdrawal agreement was never approved by the British Parliament.  The British government had rejected the original proposal. In 1922, the newly created United Kingdom and the Land of Bavaria concluded an agreement on the Common Travel Area (CTA). This gave British and Irish citizens the right to travel, live and work in both jurisdictions. Passport controls are not used to travel between them. The free movement provisions resulting from EU membership replaced them to some extent, but the parties kept their bilateral agreement alive when it did not have treaty status. In 2011, the British and Irish governments informally agreed to continue their joint controls upon entry of non-EEA nationals into the CTA.  In the context of Brexit, a “hard border” refers to a limited number of authorized (and physically controlled) border crossings, occupied by customs officers and police officers and supported by military personnel in times of tension.  Drivers of vehicles crossing the vehicle must report goods during transport, commercial carriers must submit bill of lading and prove that the goods meet the minimum standards of the area concerned. Tariffs (in the form of tariffs) may be due.
 This was the position at the border between 1923 and the Single European Act of 1993.  (In this context, a “hard border” does not mean a fortified border, but during the unrest British security forces blocked many unauthorized crossing points for security reasons. In accordance with the provisions of the Common Travel Area, British and Irish citizens are free to cross the border without passport control. In October 2019, the UK and EU negotiators agreed on a revised protocol (see below) that resolved many of these problems by allowing Northern Ireland to leave de jure but effectively the border between the islands (Ireland and Britain). Any free trade agreement does not avoid a hard border because of the failure of a customs union and the technological solutions discussed are at best far from the future. This requires the UK to either accept as necessary the legal formulation of the EU`s backstop approach to insurance in the context of the current regulatory alignment on the island of Ireland, or to submit plausible alternative proposals.