Boris Johnson's eagerly awaited trip to Dublin on Monday has prompted a flurry of speculation that a Brexit deal could be taking shape around a Northern-Ireland only backstop.

There are several reasons for this speculation.

Firstly, Johnson has precious few options if he is to abide by his promise to leave the EU at the end of October "come what may", and to abide by the law laid down by parliament.

Secondly, it was the UK-wide nature of the backstop, insisted on by Theresa May after she rejected the Northern Ireland-only backstop, that prompted the hardest objections from Brexiteers and ultimately led to Johnson’s own resignation as Foreign Secretary.

Thirdly, the EU has signalled that taking the original backstop off the shelf can be done quickly.

Fourthly, with his parliamentary majority now gone completely, the support of the DUP is no longer an issue.

But most significantly, Boris Johnson has now publicly accepted some "alignment" with EU rules in Northern Ireland.

Was a door opening?

"Can we protect the economic unity on the island of Ireland, and the gains that Ireland has won as a member of the EU’s single market," Johnson asked on the steps of Government Buildings.

"The landing zone is clear to everyone: we need to find a way of ensuring that UK [as a whole] is not locked in the backstop arrangement whilst giving Ireland the assurances it needs."

He then mentioned the suite of alternative arrangements, such as trusted traders, electronic pre-clearance of customs declarations, SME exemptions from EU customs rules and so on, before proposing "the unity of the island of Ireland for sanitary and phytosanitary purposes, in other words for agrifoods. If you can do both of those things you can get a long way through the problem."

On Wednesday, Ireland’s EU Commissioner Phil Hogan fuelled further speculation in an interview with RTÉ News.

"The British prime minister has moved away from his position…where he’s now prepared to look at divergence of certain rules and regulations on the island of Ireland vis-à-vis the United Kingdom.

"So I think there’s movement happening on both sides. Let’s see over the next four weeks how we can advance those intensive negotiations to reach an agreement."

Latest Brexit stories

Hogan suggested the EU could strengthen some of the reassurances already contained in the Withdrawal Agreement.

Article 1 of the Irish Protocol states: "This Protocol is without prejudice to the provisions of the 1998 [Good Friday] Agreement regarding the constitutional status of Northern Ireland and the principle of consent, which provides that any change in that status can only be made with the consent of a majority of its people."

Hogan said: "There are constitutional issues that … might have to be improved upon if [the Northern Ireland-only backstop] is a request that's made. Of course we can look at it. Also we have to have the North-South dimension in the context of the Good Friday Agreement, and if there’s oversight needed there I’m sure we can look at it."

But what does any of this mean?

Officials are reluctant to get into detail because of the sheer sensitivity of the issues and the excruciating lack of time before the end of October.

However, there are several ways to look at this.

Following the Varadkar-Johnson meeting, Government sources warned "significant gaps remain".

But there were signals coming out of Dublin that if the Northern Ireland-only backstop were to be revived then some kind of oversight for the Northern Ireland Assembly might be threaded into the process.

There were even suggestions that restoring the Stormont institutions would be part of an over-arching deal.

Yesterday, the London Times quoted DUP sources that the party was preparing to shift its position and agree to some regulatory divergence with the "consent" of Stormont.

"They made clear," the paper reported, "that this would not require the Northern Ireland executive and assembly, which collapsed more than two years ago, to be up and running before October 31."

On BBC Newsnight, DUP MP Nigel Dodds admitted there could be some "arrangements" of an all-island nature if they were of benefit to Northern Ireland, the EU and the Republic of Ireland.

Any such arrangements would require the consent of the Assembly, he said.

One senior source familiar with the situation cautioned that the role of Stormont in any Northern Ireland-only backstop scenario would be a tall order, in terms of the timing and how it would actually work.

"There's definitely a very ambitious aspiration around," the source said, "which says only a functioning [Northern Ireland] Assembly could actually exercise these things. That's incredibly ambitious. But on the other hand these are truly desperate times."

Figuring this out is particularly difficult because there is a stark difference between Dublin and London as to what defines a "hard border".

Is it simply the appearance of infrastructure? Or is it any divergence across a range of rules that in any way disrupts the all-island economy and North-South cooperation?

If that mismatch prevailed, it would be impossible to envisage Stormont having a clear role.

"The idea would be," said the source, "that a semi-functional assembly would allow the principle of decision-making within the Good Friday Agreement to decide what is the nature and extent of alignment [with EU rules], or non-alignment. That goes to the ambiguity of what a hard border actually is."

The idea raises numerous further questions.

What would the degree of EU alignment be? What mechanisms would be required for the Assembly to approve alignment? How would any alignment with EU rules be enforced?

While the Good Friday Agreement is designed to ensure that no one side gets its own way, and obliges the UK government to take account of both sides of the divide, there are other immediate challenges.

Firstly, issues involving the UK’s external border are not devolved to the Northern Ireland Executive.

Secondly, and more importantly, the idea that a so-called Stormont Lock could win DUP acquiescence runs into the inconvenient reality of how EU law works.

Jim Wells, the former DUP Assembly member for South Down, told BBC Radio any such arrangement which provided for an all-Ireland agrifood zone following EU food safety and animal health - but not customs - rules, "would be controlled by the people of Northern Ireland and not controlled by the bureaucrats in Europe ... That is the crucial difference."

Such notions prompt disbelief in Brussels.

Either Northern Ireland would be aligning on EU rules or it wouldn't, whether they were agrifood regulations or customs rules as well.

If EU single market rules are applying, those rules will have gone through the complex legal and political machinery upon which the EU functions.

In other words, 27 member states, the European Commission and Parliament will have negotiated the rules, voted on them, either by unanimity or Qualified Majority Voting, with the member states bringing them automatically into their own national legislations if they are regulations, or transposing them into national law if they are directives.

Once that point has been reached, if a member state, or a region of a member state, decides it doesn't like those regulations they are in breach of EU law.

The Northern Ireland Assembly would not enjoy a right that 27 member state parliaments do not enjoy.

It is true that Northern Ireland would not have ministers or MPs shaping or influencing such rules, but the very same applies for Norway and Switzerland, two sovereign countries that willingly accept the vast majority of EU single market rules in order to have access to the single market.

"There isn’t a magic rule-taking promised land," says one EU source. "What there is, is the special privileged deal for Northern Ireland in the backstop. The DUP don’t seem to be able to make the distinction."

Indeed, the UK has already tested the idea of a Stormont Lock in Brussels.

David Frost, Boris Johnson’s chief negotiator, raised the idea during technical talks with the European Commission in Brussels last week. Then on Friday 6 September, diplomats from member states were briefed by a senior European Commission Task Force official on what role, if any, Stormont might have.

The official explained there could only be three "moments" in which Stormont might be involved. Two out of three were possible, but the third was not.

The first could be when the UK agreed to sign up to the concept of the backstop. Getting the agreement of Stormont could be part of the UK’s own internal arrangements.

Secondly, agreeing jointly with the EU on exiting the backstop could also involve Stormont, since again it would be part of the UK’s own internal decision making process.

However, on the third "moment", any notion that Stormont would have to give its consent on whether or not the backstop had to apply was a problem.

"The whole purpose of the backstop is to create legal certainty," said one EU source briefed on the meeting.

"If you create the possibility where, in a world where you need the backstop, where you agree there's no other solution to avoid a hard border, then if there's a possibility that that solution is no longer operable because Stormont objects to it, then that creates huge uncertainty.

"That's bad for the whole purpose of the backstop and the Irish economy. The Commission's point is that it defies the purpose of the backstop and it doesn't make any sense."

It's also worth remembering that the Withdrawal Agreement creates a Joint Committee between the UK and EU to manage all aspects of the divorce, including the Irish Protocol.

The backstop requires alignment only on existing EU rules, and only where they are required to avoid a hard border and preserve North-South cooperation. If any of those rules are amended or replaced, then they would still apply in Northern Ireland.

However, if the EU introduces brand new single market rules, then the UK can challenge them through the Joint Committee, and London has promised to legislate to ensure that Stormont is part of that challenge.

The treaty also establishes a Specialised Committee to oversee the implementation of the backstop and to take submissions from both the North-South Ministerial Council and the North-South Implementation Bodies set up under the Good Friday Agreement.

A Joint Consultative Working Group would also serve as a forum for the exchange of information.

Sources suggest that the involvement of the North-South Ministerial Council as well as the British-Irish Intergovernmental Conference could be strengthened and given stronger political focus as part of a new approach.

"Those can be used and availed of," says a senior figure familiar with the issues. "The important point is for everybody to be clear as to be the meaning of terms and how these things work. At the moment that is not apparent."

However, the idea that the kind of creative ambiguity which helped the Good Friday Agreement over the line might be invoked would be a "category mistake."

"The GFA was within a universe which allowed for this ambiguity: joint membership of the EU, the single market, the benevolent godparents of the Americans and the EU. You could fudge things.

"The conditions in which that creative ambiguity was framed and codified have changed. It is not just a quirk of doctrinaire Brussels bureaucrats. It's something much more profound and central to how the whole thing works."

These are, as yet, ideas that may or may not have been discussed by Boris Johnson and Leo Varadkar when they met for over 30 minutes alone in Dublin before being joined by delegations.

Senior officials have downplayed the prospects for a breakthrough because of two sizeable considerations: does Boris Johnson really want a deal, and if so, can he get it through the House of Commons?

The fact that he requested a meeting with the Commission President Jean-Claude Juncker in Luxembourg on Monday has raised expectation the prime minister does want a deal.

On Wednesday night, Johnson hosted a reception for 150 Northern Ireland business people and industry groups, from the hospitality sector, to farmers, to SMEs to large multinationals.

The event was long in the making. It had been requested even before Johnson became prime minister by Trade NI, a new group coordinating the various Northern Irish business, hospitality, farming, retail and industry lobbies in the face of Brexit.

Despite the upheavals in recent weeks, Downing Street agreed that the event should go ahead, although it initially sought to exclude some of the business organisations and keep it restricted to actual employers and entrepreneurs only.

However, at the last minute Northern Ireland’s key retail, farming and manufacturing lobbies, who have been increasingly outspoken both about the dangers of No Deal and the merits of the backstop, were permitted.

"It was useful in that every single person Boris met going through the room and leaving the room said the same thing," says Stephen Kelly, CEO of Manufacturing NI. "We wish you well, but we need a deal. You can’t leave on No Deal.

"He seemed very determined to get a deal. That's the sense we got."

But this remains at odds with what Boris Johnson's chief negotiator David Frost has been pitching on his twice-weekly visits to Brussels.

On Wednesday, according to sources briefed on the discussions, the British delegation suggested that both the UK and EU should manage the border between them when it came to industrial goods.

In other words, there would be two customs and regulatory systems on either side of the border that would, over time, be enhanced by "alternative arrangements". Nothing would be written in to the Withdrawal Agreement and instead the key elements would be worked out during a transition period.

There could be no reference to the European Court of Justice, just to the EU's "legal order".

On Thursday, Michel Barnier, the EU’s chief negotiator, gave a downbeat assessment to the leaders of the political groups within the European Parliament.

"We are still ready to examine objectively any concrete and legally operable proposals from the UK," he told reporters on his way into the meeting.

Philippe Lamberts, Co-President of the Greens/EFA group in the Parliament said: "What we get from David Frost is back-tracking from the Political Declaration [on the future relationship] and removing the backstop without providing alternatives. So that’s the reality."

British sources insist London is bringing forward solutions based around customs and regulatory "facilitations", but these are so far falling well short of what Dublin and Brussels will demand, since they do not provide sufficient certainty on the integrity of the single market and on the protection of the all-island economy and North-South cooperation.

That means talk of a breakthrough via a Northern Ireland-specific backstop remains mired in the political realities facing Boris Johnson and the DUP, and the demands for legally operable and "workable" solutions from the EU.

And there is still no guarantee Boris Johnson would get it through the House of Commons.

In any event, even if he could, a technical extension beyond 31 October would almost certainly be required to pass the legislation there and in the European Parliament.

And even if the DUP were to move significantly in the coming weeks towards some kind of Northern Ireland-specific arrangement, with strengthened oversight for the Assembly and through the other strands of the Good Friday Agreement, as well as perhaps stronger language on the constitutional assurances within the Withdrawal Agreement, there are other parties in Northern Ireland which must consent as well.

"The one thing we need is time," says a senior source involved.

"That’s the one thing we don’t have. I don’t see how you can crash through a process that will bring in not only the DUP but the other parties in Northern Ireland, especially Sinn Féin, to a place where you can say: here is a solution we can live with."