At this high point in the Brexit negotiations it is coming home to many more people in Britain and Ireland that the economic consequences of a hard deal or a no deal outcome would be severe or catastrophic. The economic advantage of staying close to the EU's customs and market regimes traded off against the desire to regain lost sovereignty and limit immigration is at the core of the UK's negotiating dilemma.
If the outcome of these talks fails to gain parliamentary approval, another referendum may be the only way to resolve the issue. That option of a new popular vote should be kept open in coming months.
The pace and substance of the negotiations have been determined by deep internal political divisions over which direction the UK should take. The final round of talks in Brussels was delayed until after the Conservative party conference this week, from which Theresa May emerged somewhat stronger despite loud opposition from hard Brexiteers.
In coming days she must table proposals on Northern Ireland and the future relationship with the EU which keep the Irish border open and make clear her desired outcome. It remains to be seen whether she is willing or able to make the necessary compromises. There is still just about time to reach a draft agreement this month if she does so.
British negotiators have consistently overstated the strength of their hand in these talks and underestimated the unity of purpose on the EU side. In fact the UK position is weakened by leaving and they cannot hope to retain the benefits of EU membership after exit.
Ireland, as the most affected EU member state, benefits from that solidarity, but we have our own interest in maintaining close political and economic relations with Britain after Brexit, as well as in keeping the Irish border open and Northern Ireland close to the EU customs union and single market. The Government is balancing these extraordinarily difficult elements with skill and determination so far.
If the outcome falls foul of Westminster's parliamentary arithmetic the UK will face an historic political crisis. May's capacity to survive has stood up well so far and could see her through this greatest test by winning the vote. If she loses she will be replaced as leader, a battle which could trigger a general election. The Labour leadership would much prefer that, but the prospect of their victory may be the most important reason it will not happen.
Another referendum would then become the best way to resolve the issue. Would it be on the deal or on EU membership? There are good arguments both ways, even if – so far at least – UK public opinion has not decisively shifted.