You are absolutely correct the UK Gov does not have to agree but it already accepted the negotiating framework and a condition of this is that "sufficient progress" be made on the issue of the Irish border. It also needs to be borne in mind that unlike Yorkshire or Birmingham the undoing of this agreement has the potential to have a huge detrimental impact on communities on both sides of the Border. When the majority of the people of NI voted to remain in the EU it was not lost on them that ROI has longer life expectancy, higher incomes and higher levels of educational attainment so leaving the EU has the potential to set NI further back than is already the case.

As before The GFA is an international treaty signed by the UK & Irish Governments and lodged at the United Nations. The GFA does not contain provisions related to membership of the EU but nor does it contain provisions for the imposition of a hard border on the Island of Ireland which is what is the effect of the current position of the UK Gov. This situation can be undone either by the UK remaining in the Single Market & Customs Union or NI itself remaining in the Single Market & Customs Union or for the UK gov to signal its agreement that NI will have a compatible regulatory environment. ROI is not seeking any sovereignty status change in NI. Or taking the Foreign Secretary at his word who told the people of Northern Ireland "he does not believe the Irish border would be affected if the UK left the European Union"

Agree that no deal is not a good a good outcome but the consequences of the UK voting leave were made explicitly clear during the referendum campaign. The Irish Ambassador toured the UK explaining. With full (or partial) information England took its decision. All the Irish Gov is doing now is reminding everyone that leave has consequences and that the solution to the problems raised lies with the party proposing to break the agreement. To quote David Cameron "If the UK left the European Union, current arrangements at the Irish border could be affected It's for the people who want us to leave who need to answer these questions"

As far as I am aware their is no international legal agreement covering Yorkshire that is signed by two fully paid up member states of the United Nations. If you read the agreement it becomes clear it contains numerous provisions to cover cross border arrangements. No where in the agreement does it incl a provision for a hard border. The Irish Gov is very clear it does not agree to a hard border and it will veto any proposal that results in this scenario. https://peacemaker.un.org/sites/peacemaker.un.org...

Irrespective of who voted for what - the fact remain both parts of the island of Ireland have an agreement which was voted for by the majority in both parts of the Island of Ireland. The UK Gov can't arbitrarily vary the terms of that agreement without the consent of the other parties hence why the ROI is perfectly legitimate in saying to the UK Gov by all means if you you wish to leave the EU your business best of luck to you but if you wish to vary the the Good Friday Agreement then that is another matter. The Irish Gov has called on the UK Gov to propose arrangements that seek to maintain the substance of the agreement. To date this has not happened hence why VETO is a very real possibility. Threats of unilateral action come across more Robespierre than Edmund Burke.

And so subvert the will of the majority of Northern Ireland & break a treaty agreement.

The majority (56%) of the people in NI voted to remain in the EU in 2016. A bigger majority than voted in England to leave. Unlike Scotland, NI is covered by a treaty The Good Friday Agreement to which the UK & Ireland (ROI) are co-signatories & which is lodged with the UN. Majority (71%) of the people in NI voted for the GFA. Majority of the people in ROI also voted to change the Irish Constitution to uphold the terms of the GFA. The UK Gov could seek to vary the conditions of the GFA treaty at its own discretion but this WILL invite an Irish veto which has been the consistent position of the main political parties in ROI. Better support NI remaining in the Customs Union and Single Market and so maintain its current regulatory environment and uphold the governance arrangements as set out in the GFA which states unequivocally no change in sovereignty status of NI until unless majority in NI so agree. This argument is not just about tariffs as any cursory reading of the agreement makes plain. https://peacemaker.un.org/sites/peacemaker.un.org...