Next week, the UK government will announce its latest approach to the Northern Ireland Protocol.
It will be the latest flashpoint following six months of strife and will signpost what kind of clash we might expect in the autumn.
At the end of September, a number of grace periods will come to an end, right before the UK party conference season - a perfect recipe for another round of recrimination.
Since the end of January, the EU and UK have parted ways on their joint approach to, and interpretation of, the protocol.
Both have adopted opposing narratives and largely stuck to them: the UK claims the EU is implementing the protocol in an overly rigid, "theological" fashion that is alienating one community, and that this "unbalancing" threatens the Good Friday Agreement.
The EU argues the UK negotiated the protocol line-by-line and knew exactly what was involved and that the difficulties that have arisen are because the UK deliberately chose a hard Brexit.
Simultaneously, increasingly polarised attitudes in Northern Ireland have broken down along sectarian lines, with the business, logistics and retail sectors caught in the middle, expressing their anxieties over the new trade frictions, but by and large arguing that the protocol should stay.
A package of flexibilities announced by the EU on 30 June, including an extension to the chilled meats grace period, as well as a promise to change EU law to ensure the undisrupted supply of medicines from GB to Northern Ireland, has provided a brief but fragile truce. However, the EU and Dublin regard the UK's response to the measures as ungracious, if not antagonistic.
Both sides did agree that the announcement provided space and time between now and 30 September to negotiate a long-term solution on the movements of large and mixed consignments of food across the Irish Sea.
Officials in Brussels now wonder if that opportunity is going to be derailed by next week's announcement.
The starting positions are familiar.
The EU has proposed a Swiss-style sanitary and phytosanitary (SPS) legal agreement that would involve the UK aligning with EU food safety standards - even for a temporary period - and would eliminate 80% of the checks and controls on goods entering Northern Ireland.
While UK cabinet office minister David Frost has rejected this as a "non-starter", the EU believes there is growing support for it among businesses and politicians in Northern Ireland.
London instead wants an "equivalence" style agreement. Both sides would acknowledge each other's high food safety standards, and if the UK diverged from those standards (which have yet to change since 1 January), then the EU could increase checks and controls on the Irish Sea accordingly.
It would be accompanied by a sophisticated trusted trader scheme, allowing the auditable surveillance of food along the supply chain, from production to its arrival on Northern Ireland supermarket shelves.
The UK has submitted a paper outlining this approach to the European Commission. It is understood the paper does not suggest an arbitration mechanism, in the event of a dispute, and there would certainly be no role for the European Court of Justice (ECJ).
The EU believes an "equivalence" arrangement will only remove a small number of checks. Officials haven't closed the door on it, but they say the UK should specify what checks they are prepared to do and how far they intend to diverge from the standards they have inherited from EU membership.
"If the UK wants to do away with checks entirely there is one solution, which is an SPS veterinary agreement," says a senior EU official. "If the UK's intention is to reduce the number of checks, then they need to tell us, and we will find a solution adapted to that. Where the UK wants to reserve the ability to diverge from EU rules, then the knock-on effect of that is the presence of checks."
However, the signs are that David Frost will propose sweeping away a large number of checks at Northern ports altogether.
It's understood he will propose that only those goods that are clearly going to the South are checked, and that everything else will be the responsibility of supermarkets, who will use their own traceability systems to account for where a product is along the supply chain (from GB to a shelf on a Northern Ireland outlet).
London will insist this is still within the confines of the protocol and that it is simply a way of implementing it.
"It feels like they intend to prioritise the integrity of the UK internal market and to put in place a light touch control and inspection regime that would allow goods to flow very smoothly between Britain and Northern Ireland," says an EU diplomat.
"They're not going to propose legal amendments to the protocol and they're not going to ditch it. Rather, it would change the way the protocol is applied."
The Commission is expected to give a low-key response.
"We are always willing to have a look at [the UK proposal], and look at what we can do," says one EU official. "But it's very hard to gauge what the UK will announce. I hope they will at least prepare this announcement in a way which will not lead to surprises on our side, which will make a possible solution more difficult."
But David Frost's proposals appear to reheat ideas put forward by the UK last year and rejected by the EU.
The EU insists it has outsourced the policing of its external frontier to the UK, and that a series of annexes in the protocol - negotiated and signed by the UK - set out a precise range of checks and controls that typically apply at the frontier.
It has rejected the notion of leaving things to trust, or taking a risk-based approach to food safety. Officials say 27 member states (as well as Switzerland, Norway, Liechtenstein and Iceland) all sign up to those rules so there are no barriers to the cross-border movement of food and animals.
If the UK wants sweeping absolution from SPS checks, then it has the option of a Swiss-style agreement, officials say.
Since February, London's core complaint has been that the EU is implementing the protocol as if the UK is a normal third country and Northern Ireland is a "normal" part of the EU's single market for goods.
The EU simply cannot treat goods moving GB-NI as if they were entering from GB were the same as if they were being shipped from China to Rotterdam. To emphasise its complaint, London says SPS controls at Northern Ireland ports represent one-fifth of all checks carried out on the EU's external border.
Is this true?
Certainly, there is no other model on the EU's external frontier where one territory's supermarket sector (inside the single market) depends largely on distribution hubs in a neighbouring territory (outside the single market) for its food supplies.
In other words, the range of single market food safety checks on the Irish Sea will always be disproportionately large relative to anywhere else.
Checks roughly break down as documentary, identity and physical, and they cover customs and regulatory checks (especially on food products and live animals).
Because both sides concluded a tariff-free free trade deal last December, there are generally no tariffs payable on goods arriving from GB. However, officials need to know that goods qualify for that tariff-free access (goods manufactured with components or ingredients from other parts of the world might still face duties).
Overall, port officials are responsible for knowing what goods are entering, that they correspond to the customs and regulatory paperwork, and that nothing dangerous or banned is entering the single market.
Documentary checks involve looking at official certificates and other commercial documents that accompany a consignment.
Identity checks are a visual inspection of the goods to ensure that content and labelling corresponds to the paperwork.
Physical checks involve ensuring goods comply with the EU's SPS import requirements; these can involve health checks on animals, checks on packaging, on the means of transport and labelling, temperature sampling, laboratory testing or diagnoses where necessary.
Currently, some 15 EU customs and veterinary staff are on the ground at Northern ports on a rotational basis monitoring the checks and offering guidance.
But how extensive is the checking?
The most recent official figures were given to the Northern Ireland Assembly Agriculture Committee on 4 March.
Denis McMahon, permanent secretary of the North's department of agriculture (DAERA), told MLAs that between 1 January and 28 February this year, 13,629 documentary checks were done on paperwork accompanying food products (92% of which were products of animal origin).
During the same period, there were 11,984 identity checks and 666 physical checks.
In comparison, the Port of Rotterdam told RTÉ News that it typically carries out 44,000 physical checks per year, a figure which rose to 59,000 after Brexit took effect.
There will be more identity checks than physical checks.
Those Rotterdam checks are carried out by 70 staff operating out of five permanent inspection points for agrifood products, two for fats and oils and one for live animals.
By contrast, the inspection points in the North are still being done from portacabins since the DUP Agriculture Minister Edwin Poots suspended work on the permanent Border Inspection Posts in February.
UK officials say they are not going to order Mr Poots to resume work on the permanent posts on the basis that a future agreement may mean fewer checks, and therefore a smaller piece of infrastructure.
There is also a serious shortfall in the number of qualified vets to do the inspections.
In March, Robert Huey, Northern Ireland's chief vet, told MLAs that officials were only able to carry out between 30% and 40% of the physical checks they were supposed to.
Northern Ireland officials rightly say they are overwhelmed by the task at hand, and London says that shows the EU is being overly rigid in how the system should work.
The EU says it's only overwhelming because the UK had a full 14 months, since the protocol was signed, to build the infrastructure and train staff, but failed to do so.
EU officials also say they cannot verify the scale of documentary checks happening at Northern ports because the UK still has not provided access to its IT systems, access which was supposed to be available from 1 January.
There is no doubt that unionist anger over the protocol, and British recalcitrance, is not just over the relative numbers of physical or documentary checks.
It is about the broader risk to the free flow of goods, the "chilling effect" of GB companies no longer wanting the hassle of sending consignments of food or plants, about the barriers to the sending of parcels, and how the eventual prohibition of certain chilled meats and restrictions on horticultural products feed into identity issues.
Stakeholders told the Northern Ireland Affairs Committee in the House of Commons of persistent problems in sourcing goods from GB, with Stephen Kelly, the CEO of Manufacturing NI, saying that in a survey 77% of his members had faced problems since the protocol took effect.
The Irish government is still trying to figure out London's ultimate strategy.
"The UK is saying," according to a senior Dublin source, "whether we knew what we signed up to or not, or whether it's what we meant or not, we now all have a problem. Therefore, we have to focus on that problem.
"They're willing to take that reputational hit. But that doesn't augur well for a nation that has set itself on a path of closing trade deals all over the world. It remains to be seen whether that hurts them, but they seem prepared to take that hit, and, in some ways going out of their way to stoke up the problem."
A further criticism is that the UK is constantly expanding its repertoire of complaints about the protocol and the EU.
These relate to how the protocol was arrived at, how it is being implemented, and everything in between.
David Frost suggested to the House of Lords Protocol on Ireland/Northern Ireland Subcommittee on Wednesday that the UK agreed to the protocol in 2019 because of pressure from Remainers. "We were still a member of the European Union and people wanted us to stay in, and that was an important element of the politics that we were trying to manage," he said.
He also said the UK had introduced the Internal Market Bill (IMB) in September 2020 - which breached the protocol - in response to unspecified "threats" from the EU, that the concept of consent enshrined in the protocol was not sufficiently broad, and that the growth in North-South trade was now "a problem".
At the same time, Frost has been strangely reticent about what the threshold might be, when it comes to the degree of such trade diversion, in order for the UK to (legitimately) trigger Article 16.
"The EU is of the view," says a senior Irish figure, "that if you define the problem for us we can at least look within our toolbox and see if we can identify solutions that we can live with.
"But there isn't a clean definition of the problem. It's quite elastic and keeps getting stretched. A lot of people are increasingly coming to the view that they never really intended to apply the protocol. Alongside that is a continuation of the old game of presenting the EU as the villain."
So, a lot is at stake next week.
David Frost's plan is designed to put more pressure on the EU to radically change its approach. Brussels may just reiterate that the UK has its own choices to make, and that will be part of the negotiation running to 30 September.
But what if the EU says the plan is a complete dismantling of the protocol, based on an entirely one-sided interpretation?
In that scenario, it seems unlikely that - having raised the stakes to the floor of the Commons - Downing Street will simply revert to the SPS discussions.
The most serious outcome would be if London declares it will unilaterally proceed with its plan anyway, with the intention of creating facts on the ground.
Boris Johnson and David Frost may be banking on a weariness in EU capitals with the Irish question after nearly five years of gruelling negotiations.
But on past experience, the EU does not tend to engage in sweeping relaxations of the single market, and certainly not if they have been dictated from the House of Commons.