EU leaders are expected to conclude that not enough progress has been made in the post-Brexit trade talks to sign off on a trade deal when they meet on Thursday.
Preparations for a no-deal scenario will also continue apace.
There is cause for optimism on substantive issues such as the so-called "level playing field" – which relates to provisions to ensure the UK can access the single market without distorting competition.
However, there is far too little movement on the future of fishing rights and how the EU-UK future relationship will be governed to make this summit the do-or-die meeting as billed in Britain.
London set an October 15 deadline for a deal to be struck, but Boris Johnson said on Wednesday that he would wait for the outcome of the summit before setting out the UK's next steps.
“The outline of a compromise is not visible. If anything the EU’s position might be hardening on fisheries,” said one source close to the talks.
EU leaders Ursula von der Leyen spoke on the phone with Boris Johnson on Wednesday ahead of the summit, along with European Council President Charles Michel. "The EU is working on a deal, but not at any price," tweeted the Commission president. "Still a lot of work ahead of us."
"The Prime Minister noted the desirability of a deal, but expressed his disappointment that more progress had not been made over the past two weeks," Johnson's office said in a statement.
Meanwhile, the UK’s insistence that it will press ahead with legislation that will breach the EU-UK Withdrawal Agreement is still causing frustration. Leaders will agree that a trade deal cannot be completed unless the UK rescinds the part of the Internal Market Bill.
In addition, all EU countries are calling for “robust” dispute mechanism and governance procedures as part of the deal, partly in response to the UK being prepared to break international law.
“If the UK is willing to move, the dispute settlement mechanism will have to be very robust or it won't fly”, said an EU diplomat.
“A lot of ground has been covered but we need to see movement from the UK, especially on governance,” said another close to the talks.
The negotiations are likely to last until the first or second week of November if a deal is to be struck, according to several sources.
Employers' unions in France, Germany and Italy have meanwhile sounded the alarm in an op-ed published on Wednesday in which they warned of "cascading consequences for our businesses a well as for our citizens" in the event of a no-deal Brexit.
France's MEDEF, Germany's Dieter Kempf and Italy's Confindustria "solemnly call on the negotiators on both sides of the Channel to do their utmost to conclude an ambitious and comprehensive agreement" in time so it can be ratified and come into force by January 1, 2021.
They also called on the UK and EU to "stay committed to the Withdrawal Agreement and the Political Declaration".
Also on the agenda is the EU’s increasingly unsteady relationship with Turkey, as Turkey’s aggressive oil and gas exploration in the Eastern Mediterranean remains a major problem for Cyprus and Greece.
The return of Turkish research ship Oruc Reis to disputed waters has revived tensions with Greece and the decision of the Turkish Cypriot leader to reopen the occupied-Cypriot ghost town of Varosha has angered Nicosia.
Ankara has repeatedly ignored calls from the European Union and Athens to desist.
At the same time, voices for measures against Turkey in Brussels are multiplying.
Last month EU leaders resisted demands from Cyprus to impose sanctions against Ankara and President Erdogan. Opting instead for more dialogue and a deadline of December to take stock of progress.
EU leaders will also weigh-in on revising emissions cuts upwards. Although there is a shared goal to reach carbon neutrality by 2050, the ways and means to achieve this are still up for discussion. According to a senior EU official, leaders will discuss the "sensitivities around the table" during dinner discussions.
The European Parliament is calling for greenhouse gas emissions to be slashed by 60 per cent by 2030, while the Commission has proposed 50 per cent. This is already an increase on the 40 per cent emissions cut proposed under the terms of the Green Deal for the EU to achieve its climate targets.