Why is now a key moment in the Brexit negotiations?

Donald Tusk, the president of the European council, said last month in Salzburg that he would need to see maximum progress on the problem of agreeing an all-weather “backstop” solution for avoiding a hard border on the island of Ireland by the time of the leaders’ summit starting in Brussels on Wednesday.

Talks on the issue have been intense. At a meeting on Friday evening in Luxembourg, the bloc’s deputy chief negotiator, Sabine Weyand, told ambassadors for the EU27 via a video link from Brussels that the state of play would be assessed on Sunday, with positive results hopefully to be made public on Monday. Dominic Raab, the UK Brexit secretary, went to the Belgian capital on Sunday to seal the deal, but after he met with the EU’s chief negotiator, Michel Barnier, the bloc’s ambassadors were briefed that no agreement had been made and serious issues still remained.

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Is an agreement on the cards – and if so what is it?

The EU’s backstop proposal was that Northern Ireland would in effect stay in the single market and the customs union while the rest of the UK withdrew. This would mean that there would be no checks on goods on the island of the Ireland, but there would be on trade between Northern Ireland and the rest of the UK. It would also mean that Northern Ireland would be outside the scope of future trade deals struck by the British government, one of the chief benefits of leaving the EU, Brexiters claim.

Theresa May rejected the proposal. The UK has instead proposed that the whole of the country stay in a customs union with the EU on a temporary, time-limited basis. Northern Ireland alone would remain under single market regulations, provided Stormont agreed.

Many Brexiters do not like the idea of the whole of the UK staying in the customs union. The Democratic Unionist party does not want Northern Ireland treated differently to the rest of the UK. The EU does not accept the notion of a time-limit on a backstop. How can it be all-weather if it runs out after a period? Instead the two negotiating teams are looking to build in criteria, and a possible review clause, into the agreement so that the prime minister can sell it back home. The 21-month transition period after Brexit day could also be extended to reassure unionists that everything will be done to ensure the backstop never comes into force. If a trade deal that can solve the problem is not available after the transition period ends, they would just extend the transition.

So what happens next?

While it seems that the EU and the UK are approaching a broad agreement behind the scenes, the prime minister’s weakness at home, with both the Brexiters in her cabinet and the DUP making threatening noises, is standing in the way of progress.

Raab is understood to have suggested to Barnier on Sunday afternoon that the prime minister could not risk striking a deal now. He is said to have even opened issues that were thought to have been resolved, presumably, EU sources said, to play for time.

All negotiations are now on hold. The prime minister has been invited to address the EU’s 27 heads of state and government on Wednesday evening before a dinner. She is yet to confirm but it is likely to do so. The drama of an appeal to leaders, and then a late night discussion between them, could offer a concession to May, and a bit of momentum to help her sell a deal at home.

The risk, however, is that the leaders turn against her. They had demanded “maximum progress” by this summit in order for a November summit to be staged at which a deal could be finally signed off. The French president, Emmanuel Macron, had said he would not attend such a meeting without decisive movement by Downing Street. The leaders could instead now hold a no deal summit, to plan how they will deal with the repercussions of the UK crashing out.

That would push hopes for a deal back to a December summit. But both sides need parliamentary ratification for whatever agreement is to emerge. That will take time. And there is not a lot of it left before the UK departs on 29 March.