An internal European Commission memo has suggested that trade in agri-foods could be done on an all-Ireland basis post-Brexit, RTÉ News has learned.
The proposal would require controls between Northern Ireland and Britain, it is understood.
The memo, which is believed to have come from the office of the European Commission President Jean-Claude Juncker, says that while the trade in goods across the Irish border would have to be subject to customs controls, agriculture could be treated separately and on an all-island basis.
The memo, seen by RTÉ News, was passed to the Irish Government in February.
It is understood that Leo Varadkar was briefed on the memo before he was elected Taoiseach.
The memo, entitled "Brexit and the border between Ireland and the UK", identifies three key problems: the Common Travel Area, the cross-border trade in goods, and the trade in services.
According to several sources familiar with the memo, the idea would be to limit the disruption in the vast agri-food flows across the Irish border, especially in dairy and beef.
This is because after Brexit, Northern Ireland food products and its animal health regime would be outside the EU's regulatory sphere and would be subject to checks, thus hardening the Irish border.
However, the memo suggests that by treating agri-food on an all-Ireland basis, agri-food flows could continue.
Such a scenario would mean Northern Ireland needing to be fully compliant with EU animal health and food safety rules. That would, in theory, require checks at Northern Ireland ports on agri-food products coming in from Britain.
One senior EU source said: "My sense would be yes, that at a high level in the commission there would be a strong push to get the British to accept that at least for agricultural products, the checks should happen between the two islands."
These checks would possibly have to be carried out by EU-mandated veterinary and food safety inspectors. It is possible that they would come from the Republic of Ireland.
While EU negotiators and the Irish Government have insisted that Britain is obliged to find a solution to the impact of Brexit on Ireland, the memo gives a rare insight into the kinds of solutions that the EU itself is considering.
However, the author of the memo accepts that the idea of an all-Ireland trade in agri-foods within the EU's regulatory sphere would be controversial.
The memo acknowledges work done by the Irish Revenue Commissioners into trying to look at ways to limit the impact of customs controls for goods on the Irish border.
The memo states: "Irish customs and revenue have put significant work into designing a solution which aims to minimise the risk to the peace process. It is based on the creation of a near invisible border, with a very limited number of visible customs checkpoints, and which would predominantly rely on pre-recording of relevant information."
The memo adds, however: "This… does not address the requirements for trade in agri-food products. This note does not envisage an all-Ireland solution on trade in goods, other than agri-food goods."
According to the note, for an all-Ireland trade in agri-food to be acceptable, Ireland would first have to carry out substantive investment in customs infrastructure and that the EU would accept that Ireland fully abides by EU customs rules as they would apply on the Irish border.
An alternative to a bespoke all-Ireland agri-food trade may be avoided if the UK "as a whole" continued to comply with all EU rules and regulations on food safety.
The EU would have to certify that the UK regulatory system was "equivalent, and would require continued compliance by the UK of the food safety [rule book]…" And there would have to be an "adequate enforcement mechanism".
The memo then states that if that were not the case, then there could be "a distinct all-Ireland solution based on the distinct devolution of competence to Northern Ireland of agriculture and health [by Westminster]."
The memo adds: "This would require controls by the UK between Northern Ireland and Great Britain."
The note also spells out the risks for Ireland if there were any animal disease outbreaks in UK or problems with food safety, and why that would require strict enforcement between Britain and Northern Ireland.
"For Ireland," the memo reads, "it would entail the risk that in case of problems with the safety of UK products or disease outbreaks, it would face trade restrictions based on the fact that UK products can circulate freely within the Island of Ireland."
Essentially, if there was an animal disease outbreak in Britain that was not properly contained due to strict controls at Northern Irish ports, and the disease spread to southern Ireland, then the Irish herd would be blocked from trade with the rest of the EU.
The note adds: "Previous attempts at establishing an all-Ireland animal health policy were not finalised because of this reason. The idea would be that southern Ireland would be afraid of the consequences of its economy of the dangers that there would be contamination of what might come from Northern Ireland."
The author of the memo also acknowledges that an all-Ireland entity dealing with agri-foods would be strongly opposed by unionists.
The memo states: "As the commission's Irish interlocutors have indicated, that insisting on such a solution could harm the peace process."
The note does not explore the possibility of Northern Ireland remaining in the Common Agriculture Policy.
RTÉ News understands that the memo was passed to the then minister for foreign affairs, Charlie Flanagan, during a meeting in Brussels on 9 February.
It was also raised during a meeting between Mr Varadkar and commission officials in May, ahead of his election as leader of the Fine Gael and his elevation as Taoiseach.
Irish officials are said to have given the memo a cautious welcome. One senior Irish source described it as "welcome, but premature".
Minister for Agriculture Michael Creed this morning said that he is "not alarmed" by the memo.
He said: "Our ask is for as close as possible to the current relationship, so the content of that [the memo] doesn't alarm us", he said.
"Insofar as that paper iterates that concern and desire, we don't have anything that gives us cause for alarm."
When asked how the DUP might react to the imposition of controls between Northern Ireland and Great Britain, Mr Creed said that "they recognise the all-island nature of our economy and are very anxious to protect business, and I think the content of this shouldn't alarm anybody".
The scenario set out in the memo does not address the vast trade between the Republic of Ireland and Britain, which included 270,000 tonnes in beef exports in 2016.
The European Commission is thought to be anxious that the British government get to grips with the kinds of solutions it feels are required to solve the Irish border issue.
The Irish Government is also frustrated that the Northern Ireland Assembly is not up and running, since any potential solutions - such as those included in, but not limited to, the memo - will require political "buy in" by Northern politicians.
Both the Taoiseach and Minister for Foreign Affairs Simon Coveney have recently lamented the continued stalemate in Northern Ireland in the context of the Brexit negotiations.
Unionists are likely to respond with hostility to any solution which will require checks between Northern Ireland and Britain.