Potential for parliamentary support may increase prospect of continued negotiation

But Andrew Henderson of Pinsent Masons, the law firm behind Out-Law, said that the plan's need for customs checks between Ireland and Northern Ireland is still the biggest sticking point.

"What looks increasingly possible is that the prime minister's offer to Brussels may be able to command a majority in the UK parliament. If Johnson can prove to Brussels that his plan can break the Westminster deadlock, then it may become more appealing for the EU27 to take seriously."

"Critical now will be whether the EU is prepared to use Johnson's proposal as a starting point from which to commence a period of intensive negotiation over the coming days," he said.

UK prime minister Boris Johnson published the proposal for the basis of an EU exit deal (7-page / 117KB PDF) yesterday and asked the EU to begin a period of intensive talks immediately. The EU has not yet responded to that request.

The plan removes the need for standards and safety checks on goods on the island of Ireland by keeping Northern Ireland in the EU's single market. But it takes the province out of the EU customs union, which means that customs checks will be needed.

The UK government has proposed that technology will help with those checks and that they can take place at locations that are not precisely on the Irish border, but the EU and Ireland are thought to be unlikely to agree that this removes the Irish border question entirely.

Dublin is opposed to any border infrastructure and has said that creating border checks risks undermining the Good Friday peace deal and is likely to lead to a resumption of hostilities in Northern Ireland.

The EU's response to the proposal has so far been measured, but Henderson said that does not necessarily indicate that agreement will be possible.

"That the EU27 did not immediately reject his new proposals, may afford the prime minister some grounds for optimism. However, reaching a ratifiable deal from here remains far from assured," he said. "Neither the EU nor the UK government will want to shoulder the blame in the event of no deal, so the EU will be at pains not to dismiss out of hand any proposals at this stage, even if they believe them to be unworkable or unacceptable. A need to be seen to consider Johnson’s ideas seriously may account in part for the tempered response so far."

“Time will pile pressure on any further negotiations," said Henderson. "Given the UK government’s commitment not to seek any further extension, despite the legal requirements of the Benn Act, the timetable for ratification before 31 October remains exceptionally challenging.”