The readmission agreement agreed in the current withdrawal agreement would temporarily keep Northern Ireland in the internal market, which would involve some controls on goods entering Northern Ireland from Britain. But the whole of the UK would remain in a common customs territory with the EU. The insurance deal was negotiated by Theresa May because the then Prime Minister believed that no British Prime Minister could accept the EU`s first proposal: a backstop in which only Northern Ireland remained in EU customs territory. This would mean that a customs border would be drawn in the Irish Sea. May called it a threat to the UK`s constitutional integrity. The terms of the backstop were finalized in November 2018. Sinn Féin, SDLP, Alliance Party of Northern Ireland and the Green Party in Northern Ireland all support the backstop.  The Irish border has been described as a “backstop” by both the UK and the EU because of its importance to the peace process in Northern Ireland. The Good Friday Agreement of 1998 was a key element of this peace process. One of the three main points of the agreement was the creation of infrastructure for “North-South cooperation” between the Irish government and the new Northern Ireland Assembly. On 17 October 2019, it was announced that UK and EU negotiators had reached a “new” or “revised” agreement on the Irish border, which put an end to The Irish backstop proposal. You can read the new rules for Northern Ireland here. In order to avoid a border between Northern Ireland and the rest of the United Kingdom, Article 6 of the Northern Ireland Protocol proposes that the United Kingdom and EU customs officers act as one from the end of the transition period (December 31, 2020) until the parties agree on a satisfactory alternative for both parties.
 The single customs territory between the UK and the EU does not apply to fish products: for example, fish transported from Britain to Northern Ireland would be subject to EU tariffs in the absence of a separate fishing agreement.  The UK Government foresees the withdrawal of the United Kingdom from the internal market and customs union, which requires the return of a series of controls on goods crossing the border between Northern Ireland and the Republic of Ireland. The “backstop” as a substitute must ensure that such controls are not mandatory between the end of the silent transitional period proposed by the withdrawal agreement and the beginning of a promising future economic relationship. If the UK were to leave the EU without “any agreement” (if the draft withdrawal agreement is not approved by Parliament), Northern Ireland (under the UK) would have different customs and regulatory standards than Ireland (under the EU). This means that customs controls on goods must be imported at the border, which could create a “hard border” with physical infrastructure such as cameras or guard posts. This would undermine the principle of North-South cooperation as defined in the Good Friday Agreement. What is the big picture behind the Brexit backstop drama? Prime Minister Boris Johnson says he is determined to “get rid” of the backstop, calling it “anti-democratic.” This article is now obsolete as it refers to the Irish backstop as stipulated in Theresa May`s withdrawal agreement in November 2018. It reflects the situation until August 2019. Parliament voted for the first time against the withdrawal agreement in January 2019. Following the DUP`s objections, Mrs May agreed on a backstop in which the whole of the UK would indefinitely maintain a very close relationship with the EU, namely the maintenance of the customs union. The withdrawal agreement and the new “instrument” on the backstop were rejected by Parliament in March 2019.