By Wednesday afternoon, it will be clear whether Boris Johnson will have a deal to put to parliament on its “super Saturday” sitting or not. Michel Barnier, the EU’s chief negotiator, will inform members whether the prime minister has conceded enough on the Irish border for there to be a draft treaty to present to leaders when they hold a summit on Thursday.

Are we close to a deal?

The prime minister has made a series of major U-turns in recent weeks. That has given EU officials some hope he will continue in this vein. A final push has been demanded by Barnier and EU sources are confident Downing Street will deliver. There are nerves in Berlin and Paris at the pace of developments but the European commission is keen to get a deal done.

What does the EU want?

Barnier has said the UK needs to table a legal text, and it needs to be based on the February 2018 Northern Ireland-only backstop. That proposal – rejected by Theresa May as a constitutional outrage that no British prime minister could accept – would keep Northern Ireland in the single market for goods and the EU’s customs territory. The arrangement would cease to be in force if a future trade deal offered an alternative solution for avoiding a hard border on the island of Ireland.

Barnier is open to tweaking that model, however. A consent mechanism, under which Stormont has a say over alignment with the EU, could ensure that both nationalist and unionist communities give their approval for continued alignment with the EU. On the tentative deal on customs, Northern Ireland could de jure remain in the UK’s customs territory rather than the EU’s. But Northern Ireland would de facto remain under the EU’s full customs code. It would in practice be a thick border in the Irish Sea.

Could it go wrong?

Yes. A similar deal was killed off by the Democratic Unionist party and the Brexiter European Research Group MPs in 2018. But both seem to be giving Johnson more leeway than they afforded May. Any arrangement that creates checks and controls, and potentially a tariff border between Britain and Northern Ireland, is problematic. But the UK would establish a rebate system to ensure businesses in Northern Ireland are not financially disadvantaged. They could also arguably claim that the UK, “whole and entire”, would leave the EU’s customs territory.

What if a deal is not agreed by the summit on Thursday?

There are two possibilities: deadlock if Johnson decides to attack Brussels for intransigence, or further negotiations to talk around the problem next week. The latter would open up the possibility of a second EU summit, perhaps on 29 October, for a potential deal to be signed off by leaders. A Brexit extension beyond 31 October is inevitable either way.

What is the most likely outcome?

For all the noise from Downing Street, Johnson has been a pliant negotiator with Brussels in recent days. There is some evidence that he now wants to put a deal to parliament on 19 October, come what may. If the last three years of Brexit have taught us anything it is that fudge, delay and prevarication are always the most likely course. But EU sources are confident a deal is there to be had this week given the UK’s sudden flexibility.