外交官们预计，第一个后果将是取消11月的特别峰会。法国总统埃马克龙(Emmanuel Macron) 10月份在萨尔茨堡的一次峰会上表示，如果脱欧没有取得进展，安排这样一场会议就不值得，因为他不会参加。一名欧盟高级外交官表示：“如果特雷莎·梅现在不能在这些问题上给出明确的指示，那么她没有理由在11月能够做到这一点。”
Brexit deal， muddle or disaster： the 3 scenarios the UK faces
Brexit negotiations have entered the most high stakes period since the UK’s 2016 EU referendum. Expectations of a breakthrough are so elevated that a failure may prove spectacular.
Before the weekend is out， negotiators want to agree a complete draft treaty， defining the terms of Britain’s departure， a 21-month transition， and the solution to Northern Ireland’s border conundrum.
But should a deal could prove elusive， senior officials on both sides fear it will trigger a jolt in markets， upheaval in Westminster， and a frantic phase of European diplomacy.
“I’m optimistic but it’s hard to imagine how this will be a completely smooth process，” said an EU member state official overseeing Brexit preparations. “A breakdown and crisis can provide sudden energy.”
Those preparing for the coming weeks — including an EU summit on Wednesday — foresee three main scenarios： a clean deal; a serious crisis; or an unpredictable muddle.
The clean deal
If there is one clear deadline in the coming days， it is a meeting of so-called “Sherpas” on Monday， which is preparing for the summit of the EU’s 27 remaining member states on Wednesday night. If an agreement is not in hand by Monday there will not be enough time to prepare the summit.
Even with a deal this weekend， the Brexit negotiations will not be over. The two sides hope to finish a draft of the withdrawal treaty — the only legally binding agreement between Britain and the EU that will remain after Brexit day. But that text will remain ad referendum — subject to final agreement.
That is because the accompanying “political declaration” on future relations will be a work in progress. A skeleton version is expected to be published on Monday to serve as the basis for a final stretch of talks ahead of a special summit in mid-November.
The declaration is crucial for Theresa May， the British prime minister. She wants the document to set out such an ambitious vision for UK-EU relations that a “backstop” plan to avoid a hard border with Ireland would only be needed temporarily， if at all.
The declaration must also show that a UK-wide customs union would apply for as long as a backstop is needed; the terms of the customs arrangement will largely be outlined in the declaration on future relations.
One senior EU diplomat said Wednesday evening’s dinner meeting may consider whether to offer new guidance to Michel Barnier， the EU’s chief Brexit negotiator， regarding such a customs union.
This would flesh out the kind of provisions — on issues such as state aid， labour and environmental rules — that would be expected of a customs union to ensure a “level playing field” between the UK and the EU.
The serious crisis
Without what Mr Barnier describes as “decisive progress” on the withdrawal issues — and especially the Irish border— Britain is likely to be in for a bumpy ride.
Diplomats expect the first consequence would be the cancellation of November’s special summit. Emmanuel Macron， the French president， told a summit in Salzburg in October that without progress on the backstop it would not be worth arranging such a meeting， since he would not come. “If May cannot give a clear indication on these points now， there is no reason why she would be able to in November，” said one senior EU diplomat.
If there is no breakthrough in coming days， EU leaders would encourage British officials to spend more face-time with Mr Barnier so that a deal can be ready in time for a regular EU summit in December.
The delay would rattle markets and leave little time for Westminster to ratify an agreement， should one be reached. The dark mood would be reinforced by both sides pressing forward with no-deal contingency plans， including by spending money on preparations for a hard exit.
An unpredictable muddle
Britain’s apparent willingness to agree a withdrawal treaty text — even before the statement on future relations is finished — is propelling negotiations this week. EU negotiators had previously expected Britain to hold back some of its cards — especially regarding the Irish border — until the final hours of the negotiation.
Mrs May might still decide on such a manoeuvre at the last moment for domestic political reasons， or to maintain some negotiating leverage in the final straight.
That would leave talks in a diplomatic limbo. On the one hand， the EU would recognise significant progress， with everything agreed， except perhaps some details relating to Northern Ireland. But such movement may fall short of what Donald Tusk， the European Council president， refers to as “maximum progress”.
The benchmarks are in the hands of the EU leaders — and their top negotiator — to assess. “The most important judgment will be Barnier’s，” said one senior EU figure involved in the process.