Namely, the Port of Liverpool has an existing Border Inspection Point for exports outside of the EU. Stranraer could be used to process checks for ships using the nearby Cairnryan port, which has limited space.

Under the details of the new withdrawal deal, EU representatives could potentially act as customs staff at the relevant ports. It is further said that there is a proposal for smaller pop up labs at ports with mobile testing labs for health checks on food exports.

Industry figures quoted to BBC after leaks from within Whitehall listed "facilities for high levels of checks and controls" as one of "a number of challenges" with delivering the PM's Brexit deal by December 2020.

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What is more, one senior industry figure said that there was an "implicit understanding" that such checks for food products would be in Great Britain, partly because of sensitivities about new infrastructure representing a form of trade barrier within the UK; and partly to further avoid having to send back foodstuffs not compliant with EU single market rules.

The precise nature of the border checks depends on how aligned the UK remains with the EU; the decisions of the Joint Committee of the EU and the UK to be set up after Brexit, and whether UK authorities are willing to accept security and revenue risks in order to keep trade flowing. Technology could also help alleviate some of the checks.

Paperwork and some checks will be required for agri-food imports into Northern Ireland from Great Britain, on the regulatory compliance of goods with the single market, and for trade tariffs for goods deemed to be at risk of being taken to the Republic of Ireland.

Goods remaining in Northern Ireland should have their tariffs repaid by the UK government, but a system for this is yet to be implemented.

On their part, the prime minister has also argued that only goods destined for the EU would face checks, but the industry says even verifying that would mean checking some intra-UK trade.

Earlier in the year, the majority of goods arriving from the EU were to be allowed into Britain without full customs checks for at least three months if UK left the bloc without an exit deal.

In April it was stressed that the UK customs system may not be ready for Brexit and it could be three more years before it is, as Peter MacSwiney, chair of the Brexit committee at the Joint Customs Consultative Committee (JCCC) has previously stated.