The text of the agreement has to be discussed in 27 national capitals, if EU leaders are to sign it off at a summit on 14-15 December. “The less time we have before the European council, the more difficult it becomes to run the text through 27 national administrations and get an agreement,” said one. “It is [the UK’s] decision to leave it to the last minute and it is [the UK’s] risk.”

Juncker and May attempted to put a brave face on the spectacular collapse of their plans in press statements at the end of the day. The commission president praised May for being a “tough negotiator” who was energetically fighting for Britain’s interests.

May insisted that progress was in sight and that the negotiators would reassemble by the end of the week, with Wednesday evening now sketched into officials diaries. “On many of the issues there is a common understanding and crucially it is clear we want to move forward together”, May told reporters. “There are a couple of issues, some differences do remain, which require further negotiation and consultation. And those will continue but we will reconvene before the end of the week and I am also confident we will conclude this positively.”

Government sources made clear that there were two key sticking points yet to be solved in the negotiations with the EU27 - the role of the European Court of Justice when it came to citizen rights and the Irish border.

Eoin Treacy's view

The Democratic Unionists (DUP) must be thanking their lucky stars that Theresa May needs their help to keep her government afloat. She has little choice than to consider their interests in the negotiations. As I see it there are five potential options for the question of the Irish border to be resolved. 

The first is that the UK exits the EU but stays inside the customs union. That will enrage the Brexit camp which will, rightfully see it as a negation of the vote to leave in the first place but it remains an option and would allow the UK some leeway to negotiate outside the EU. 

The second is that a special case is made for Northern Ireland staying inside the customs union but not the rest of the UK. Scotland and London will want to participate in that deal too but it is not exactly palatable for Northern Ireland’s unionist parties.  

The third is to cut Northern Ireland loose so it becomes an autonomous state which the DUP will absolutely not stand for. 

The fourth is no deal and the imposition of a border. 

The fifth, and most unlikely, is Sinn Fein finally takes its seats in parliament in exchange for a path to a united Ireland. That would give the Conservatives 325 seats so exactly half.

There is no easy answer to this question but I consider the 1st option or some variation on it, to be the most likely potential outcome.