The European Commission has challenged the UK to align with EU food safety rules as a "far-reaching" solution that would remove the need for most of the checks and controls on food products entering Northern Ireland from Britain.
A senior EU official said that the UK could consider aligning with EU rules until it has negotiated its own future trade agreements with other third countries.
Brussels believes the UK is resisting aligning with EU food safety rules so as not to hinder a free trade deal with the United States.
The official said that while the EU was stretching the flexibility of EU food safety and animal health rules to "breaking point" in order to make the Northern Ireland Protocol more manageable, the UK could itself go for a "structural solution" which would substantially reduce the number of checks and controls on goods crossing the Irish Sea.
The official said without a structural solution, such as aligning with EU rules, finding flexibilities within the Protocol would be "piecemeal".
The UK has repeatedly ruled out a veterinary agreement that would involve the UK sticking to EU rules into the future - known as dynamic alignment - preferring an equivalence-based approach, whereby both sides would recognise each other's food safety and animal health rules.
An EU official said if the UK did not wish to adopt an alignment approach, then the EU expected it to implement the Protocol "as agreed".
"Our position is simply that we ought to now implement what was agreed," the official said. "If what we've agreed is implemented properly then it would be of huge benefit to Northern Ireland which would be the only part of the UK to have access to the EU's single market and the internal market of the UK.
"If the UK considers that the checks that will be required as a result are a problem, then there is a solution, a permanent solution, [or] a temporary solution...pending the existence of future UK trade agreements."
The official added: "But that's a decision for the UK to take. Otherwise we just stick to the normal implementation of the Protocol that had been agreed and that's fine with us."
Under the Protocol, the EU's sanitary and phytosanitary (SPS) rules, covering food made with animal-derived products, live animals, including pets, and plants, apply in Northern Ireland.
That means that when the Protocol is fully applied, such products coming from Britain to Northern Ireland will need to comply with EU rules.
The official said the EU was looking at ways to make it easier for those with guide dogs to cross from Britain to Northern Ireland without the full range of certificates, such as those for rabies, which normally apply to pets entering the EU from third countries.
Flexibilities were also within reach for some plants, and the tagging of live animals that move back and forth across the Irish Sea, the official said.
London has complained that the full implementation of these rules is causing disruption to everyday life in Northern Ireland.
However, the senior official said the burdens of the Protocol were down to the UK's choice to have a more distant trading relationship with the EU.
"Some of the practical issues are the everyday life consequences of the bigger structural choices made by the UK," said the EU official.
"Looking for flexibility within the Protocol and looking for flexibility within EU legislation, some of the requests of the UK would stretch that flexibility beyond breaking point. That's why we say only a structural shift in the position of the UK can avoid, or lead to a reduction in the number of, checks."
The UK is seeking an equivalence agreement based on an agri-food deal the EU has with New Zealand.
However, the EU says that the volumes of trade between the EU and UK are much broader and deeper, and that the New Zealand arrangement would reduce, but not eliminate, checks and controls on Britain-Northern Ireland food consignments.
The European Commission has taken legal action against the UK for unilaterally easing some of the requirements of the Protocol.
The UK was issued with a letter of formal notice, the first step in legal action, on 15 March. London requested an extension in the period granted to reply, meaning the Commission is expecting a response by 15 May.
According to a choreography set out by the official, the UK response to the legal action could coincide with a clear awareness on both sides of where solutions can be found, and where a gap remains.
It is hoped a joint document could then be produced by both sides by the end of May or early June.
"By the middle of May most of the elements will be known and will have been discussed," says the official. "Then it's a question of more technical work to see how this can be reflected in a joint document."
In technical talks between both sides, the UK has been pushing for the EU to take a more risk-based approach to the Protocol, meaning that categories of food entering Northern Ireland from Britain would be assessed on a case-by-case basis as to the extent to which they might pose a clear risk to the integrity of the EU’s single market, or to consumer health.
However, officials say that the EU has its own rules on what poses a risk, and that its food safety regime was about what risks exist and how to manage them.
Officials point out that the UK, through the Protocol, had agreed that Northern Ireland abide by those same rules.
"The fundamental point is that SPS legislation in itself is about evaluating how much risk you're prepared to accept, and that in setting its SPS rules the EU has made a choice as regards the kinds of risks it sees exists, and how to manage them," says a senior official.
"The Protocol... enshrines that legislation in its annexes and requires that the UK implement them."
For this reason, said the official, the UK could consider dynamic alignment, even on a temporary basis until it had concluded free trade deals with other partners.
The official pointed out that under an agreement reached last December, the UK had committed to remaining aligned with EU food safety rules for the duration of a number of grace periods, which the UK unilaterally extended in March.
"We think that rather than look at an approach based on risk, or the existence of it, or not, the best way is simply to look at this through a positive perspective, assume that the UK and EU have a clear joint interest in remaining aligned on high standards on SPS rules, [and that] not only will that benefit the citizens in terms of their health but it will also have the added benefit of facilitating the implementation of the Protocol.
"Alignment on SPS rules will take away the need to have checks to a very large extent on goods between GB and NI."
A UK source has reaffirmed London's preference for an equivalence agreement and drew attention to its continuing support for businesses adjusting to the new trading arrangements through the recruitment of more vets to certify exports and to financially support companies though the SME Brexit Support Fund.