The DUP and Sinn Féin leaders have sent a joint letter to the European Commission describing as "unacceptable" the alleged threat to the continuity of existing food supplies to Northern supermarkets once the Northern Ireland Protocol takes effect.

The letter, seen by RTÉ News, and signed by Arlene Foster and Michelle O'Neill, highlights the problem of the need for checks and controls on food products entering Northern Ireland from Great Britain from 1 January and how that might impact on the supply of food to supermarket chains.

The First and Deputy First Ministers write: "It is hard to imagine a more fundamental aspect of everyday life than the purchase of daily food supplies. Hence, we would ask you to recognise how important it is that the current consideration of the detail of how the Protocol will be applied takes our unique context into account." 

Under the protocol, food and animal derived products entering Northern Ireland from Great Britain will be subject to the EU's food safety regime, meaning that so-called sanitary and phytosanitary (SPS) checks will be required on a range of products destined for supermarket shelves.

EU and UK officials have been grappling with the issue through the Joint Committee, set up under the Withdrawal Agreement to implement the Northern Ireland Protocol.

Industry representatives say that thousands of goods within lorry containers could require EU export health certificates in order to qualify for entry into Northern Ireland.

Writing to the EU's representative on the Joint Committee, European Commission Vice President Maroš Šefčovič, the First and Deputy First Minister said: "Last week, there was a meeting that included representatives from our main supermarkets here.

"These representatives have emphasised how critical the current situation is, with a real threat to the continuity of the supply of existing food and other products to our market unless these issues are urgently addressed and solutions found."

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They added: "This is an unacceptable situation for us to be in, especially so late in the process."

The two leaders say they welcome the "constructive work" both sides have been engaged in and acknowledge that they are seeking "a pragmatic application of the principles and purpose of the SPS controls".

They refer to the "best endeavours" clause within the protocol, which they say "can and must secure an outcome which guarantees the normal flow of agri-food products to our people".

The ministers say any outcome that would lead to "material price increases and/ or reduced choice for consumers would be an unacceptable consequence which cannot have been the intention of anyone when the Withdrawal Agreement was settled".

The letter states: "We recognise clearly the absolute importance of the SPS controls to the European Commission and the Member States and we would want to make it clear that we are not asking for anything that would create any form of health risk.

"We are hopeful and confident that with goodwill and pragmatism an agreed approach can be settled and applied. In any case, we are doing all that is possible to ensure that the necessary processes will be in operation to ensure goods can flow through our ports of entry at the end of the Transition Period."

The UK has been seeking blanket derogations or facilitations covering food products moving from Great Britain to Northern Ireland.

However, the European Commission and member states have been concerned that EU food safety rules should be respected in order to protect consumer health.

After 1 January, any goods entering Northern Ireland from Great Britain will in theory be able to circulate throughout the single market. Any goods that are food products or derived from animal products will not have been produced under EU food standards.

There have been reports that some UK supermarket chains may close their outlets in Northern Ireland or reduce the range of products destined for Northern Ireland.

The letter states: "We look forward to an urgent resolution of these issues, as businesses here need clarity as soon as possible on the precise detail of the changes that will affect them. So we would look forward to seeing significant decisions resolved and confirmed at the next meeting of the Joint Committee."

Ms Foster and Ms O'Neill state that some of the issues will be made simpler by the conclusion of a free trade agreement, "but urgent action to resolve the issues in the Protocol need not and should not be dependent on that process".