But what is the backstop and why was it such a sensitive point? Mr Barnier told French radio station RTL: "The time is too short to find an alternative to the Irish backstop and the UK`s divorce treaty with the European Union will not be reopened to negotiations."  On 29 March 2017, Prime Minister Theresa May launched the two-year Brexit negotiation process, with a deadline set for Article 50 of the EU Treaty.  In response, the other EU countries (EU27) have published their "phased" negotiating strategy, which has postponed all negotiations on future relations with the UK (the non-binding "political declaration") until a binding withdrawal agreement is reached: others have proposed a unilateral deadline or exit clause from the backstop to prevent the UK from being subject to EU rules. But in recent days, Johnson rejected this proposal and said that the backstop should be completely abolished. The "backstop" agreement reached in December 2017 between the EU and the UK indicated that Northern Ireland would effectively remain in the EU customs union without another solution for the border. To avoid this, the EU has included a "backstop" in the withdrawal agreement negotiated with May. It is an insurance policy that ensures that the status quo will remain on the Irish border after Brexit, leaving the UK in one country. It is possible to conclude a trade agreement on customs territory." In addition, Northern Ireland will be aligned with certain parts of the internal market with respect to certain rules and regulations. The Irish backstop is essentially a safety net that would prevent the reintroduction of a hard border on the island of Ireland after Brexit. And because the UK and the Republic of Ireland are both members of the EU, both countries have been and are currently free to travel between the two countries, without any checkpoint or passport checks.
But what will happen if Britain leaves the 28-nation bloc on 29 March remains a mystery. The "backstop" would have required northern Ireland to remain in certain aspects of the internal market until an alternative agreement between the EU and the UK is concluded. The proposal also provided that the UK as a whole would have a common customs territory with the EU until a solution was found to avoid the need for customs controls in the UK (between Northern Ireland and Great Britain).