The twists and turns of Brexit - after more than three years of negotiations - will dominate an EU summit on Thursday, amid signs of an emerging deal.
Negotiations to nail down complex arrangements for Northern Ireland, the main sticking point, appear to have produced a draft acceptable to the EU.
But UK PM Boris Johnson does not have a majority in parliament and relies on unionist Northern Ireland MPs.
They have issued a statement opposing the draft "as things stand".
The British pound fell considerably moments after the statement by DUP leader Arlene Foster was released.
The summit is due to begin later on Thursday.
Frustration is palpable on both sides: Mr Johnson wants the UK to leave the EU on 31 October "do or die"; and in Brussels the BBC's Katya Adler tweeted that "EU diplomatic and political sources I speak to are sooo fatigued with this process".
The EU has already extended the UK's Article 50 withdrawal negotiations twice.
But the rush to finalise a deal this week is causing alarm in some quarters.
EU officials expect another extension - perhaps shorter than three months - will still be needed to resolve legal technicalities.
Two anxieties loom large for EU governments:
- the chaos that many fear a no-deal Brexit would bring
- and the amount of EU time and energy eaten up by Brexit
They have other pressing issues to deal with, such as eurozone integration, the migrant crisis and climate change.
On Wednesday evening, Tony Connelly of Irish broadcaster RTE tweeted that "all outstanding issues with the exception of VAT are now resolved", quoting an unnamed EU source in Brussels.
So, a draft Brexit deal could be signed off at this summit. But there are doubts over whether the PM will get a majority at Westminster to approve it.
A cross-party group of MPs opposed to Brexit was in Brussels on Wednesday, insisting that any deal should be put to a new UK referendum.
Pro-Remain MPs argue that in 2016 no such deal to leave both the EU single market and customs union was put to voters.
Why has Brexit focused so much on Northern Ireland?
Both the EU and UK pledged to prevent the return of a "hard" border in Northern Ireland.
But when the UK leaves, that border becomes an external border of the EU.
The Republic of Ireland has warned all along that any customs checks on the border would jeopardise the 1998 peace deal - the Good Friday Agreement.
But once the UK leaves the EU customs union and single market the risk, as Brussels sees it, is that the porous border could attract smuggling and fraud.
The EU customs union means:
- no customs duties are paid on goods moving between the 28 member states
- all apply a common customs tariff for goods imported from outside the EU
- goods legally imported can circulate throughout the EU with no further customs checks
The single market means the EU is treated as one territory, with no regulatory obstacles to the free movement of goods and services inside the bloc.
The deal taking shape appears to keep Northern Ireland within a UK customs union, but aligned with EU regulatory standards.
To avoid land border checks, EU tariffs could be imposed on goods arriving at Northern Ireland ports and Belfast airport from the UK.
Refunds could be claimed for goods which stay in Northern Ireland, and do not enter the EU via the Republic.
It all means extra costs and paperwork. There will be many sceptics in Northern Ireland, where a majority voted to remain in the EU.
Why is the 'level playing field' an issue?
The "level playing field" was included in the Withdrawal Agreement negotiated by Boris Johnson's predecessor Theresa May.
It was a commitment to abide by certain EU rules in exchange for market access. Those rules include environmental standards, workers' rights and services.
But Mr Johnson insists the UK must be free to sign future trade deals globally without being tied to EU rules.
In that case, the EU argues, the UK cannot expect any privileged access to the single market.
Chief negotiator Michel Barnier has told the UK repeatedly that it cannot "have its cake and eat it" or "cherry pick" from EU agreements once it has left the bloc.
German Chancellor Angela Merkel raised the issue recently, warning that "Britain will develop into another competitor on the doorstep of Europe".
Could UK politics still block or delay Brexit?
Boris Johnson said he would "rather be dead in a ditch" than agree to extend Brexit beyond 31 October.
But his government is now legally obliged to comply with the Benn Act. It requires the government to request another extension to Article 50 if Parliament has not approved a withdrawal deal by 19 October.
The postponement of Brexit would be until 31 January.
The fate of any Brexit deal is uncertain, not only because Theresa May's deal was rejected three times by the House of Commons.
A deal would also require the unanimous approval of EU leaders and a "Yes" vote in the European Parliament.
And an early UK election is now widely expected, adding to the uncertainty.
Whatever happens in the Brussels negotiations, Brexit remains a hugely divisive issue in the UK.