The Belfast Agreement (“Good Friday Agreement”) does not state that the border between the Republic of Ireland (RoI) and Northern Ireland must be open or that there must be the same standards for goods (conformity – ‘CE’) or that tariffs and excise duties should be the same across the border. However, the UK-EU Withdrawal Agreement does say that the border must be open and represents a significant further step towards the unification of Ireland.
Whether this enhanced RoI/NI unification was a brilliant play by the Irish negotiating team or a deliberate subversion of Brexit by the British team is a moot point. To repeat: the Belfast Agreement does not specify open borders.
How did we get a position where all parties seem to be assuming that the Belfast Agreement is incompatible with Brexit? The BBC, which is supposed to represent the interests of the British People, should have picked up the fact that NI is not a problem. The other broadcasters should also have spotted this fact.
What has occurred is that the EU managed to get our foolish (or subversive) negotiators to agree that there will be no border between NI and RoI at the start of negotiations. It was the 2017 position paper on the UK’s withdrawal from the EU that introduced the new agreement that involves open borders between the UK and the RoI. In paragraph 49 of the position paper it states that the “United Kingdom remains committed to protecting North-South cooperation and to its guarantee of avoiding a hard border”. Avoiding a hard border is not actually part of the Belfast Agreement but the British team gave this point to the RoI and EU for free.
Having extended the Belfast Agreement by adding the idea of “no hard border” to it the British team then pre-empted all of the future negotiations. Paragraph 49 then goes on to say that the UK accepts the Customs Union and even the Single Market if the EU so wishes :
“The United Kingdom’s intention is to achieve these objectives through the overall EU-UK relationship. Should this not be possible, the United Kingdom will propose specific solutions to address the unique circumstances of the island of Ireland. In the absence of agreed solutions, the United Kingdom will maintain full alignment with those rules of the Internal Market and the Customs Union which, now or in the future, support North-South cooperation, the all-island economy and the protection of the 1998 Agreement. ”
All the EU negotiators needed to do thereafter was to play hardball and the UK would be bound to accept the Customs Union at the minimum. In other words the Brexit negotiations began by accepting that the UK would remain in the Customs Union and possibly even the Single Market.