Johnson said during a telephone conversation with Varadkar that his government would “never put physical checks or physical infrastructure on the border” between the British province of Northern Ireland and the Irish Republic, even without an agreement between the U.K. and the EU on 31 October, the Foreign Ministry stated.

The new Conservative leader repeated that he wanted a withdrawal agreement with the EU but without the backstop, a last-minute mechanism aimed at avoiding a return to a hard border in Ireland, where the 500 kilometres separating Northern Ireland and the Republic of Ireland will become the only land border between the EU and the UK.

However, Varadkar told his British vis-à-vis that the backstop was necessary and that it stemmed from the UK’s decision to withdraw from the EU. He stressed that the EU was “united in its view that the withdrawal agreement” concluded with former British Prime Minister Theresa May in November “could not be reopened,” a statement from Dublin said.

Alternative arrangements could replace the backstop in future, but “thus far, satisfactory options have yet to be identified and demonstrated,” it added.

According to the November agreement, the backstop would take effect after a transition period if no other solution is found between the EU and the UK by mid-2020. It consists of creating a single customs territory between the EU and the UK within which there would be no quotas or customs tariffs for industrial and agricultural goods.

Under the backstop mechanism, Northern Ireland would also comply with a limited number of rules of the European single market, such as sanitary norms for veterinary controls.

However, some Brexit advocates and their Northern Irish ally in Parliament, the small DUP party, are totally against this solution which, they feel, would harm the integrity of the UK and its market.