Supermarkets will be permitted to continue to supply Northern Ireland shops without special Brexit checks that will kick in, deal or no deal, on 1 January.

In a concession by the EU, Sainsbury's, Marks & Spencer, Asda and other trusted traders in the food sector will be given a waiver potentially running to a number of months before checks apply.

It means sausages, burgers and cheeses will not be examined individually at ports, addressing recent concerns from Sainsbury's that it would have to curb meat, dairy and fish supplies because of the Brexit checks.

There had been fears expressed by traders that every item in a food truck would be subjected to checks, with the example of a ham and cheese sandwich requiring two health certificates for each ingredient.

"There will be a grace period; trusted traders will not be subjected to the checks during a grace period," said a government source. "It will not apply for very long but they won't be required to do the full checks. The point is, everyone has to comply with the sanitary and phytosanitary checks, but we were determined to ensure food supplies were not interrupted and got this concession from the EU."

Earlier reports that businesses in Northern Ireland would be required to fill out Brexit paperwork when sending their goods across the Irish Sea to Britain, a year after Boris Johnson told them they could put export forms in the bin, have been denied.

The threat that they would have to complete export and exit declarations has been lifted, it has emerged. The only checks will be on a limited list of items, including endangered species and blood diamonds.

Sources said the concession was made as part of a package of arrangements hammered out in the UK-EU joint committee in exchange for the UK dropping its law-breaking Brexit clauses in the internal market and taxation bills. They will be unveiled in the House of Commons by the committee's co-chair and cabinet minister Michael Gove later on Wednesday.

There has also been a deal allowing 15 EU officials to be permanently based in offices in Belfast to help traders get to grips with the new system and monitor enforcement by UK officials. Their presence represents a U-turn for the government, months after it told Brussels they could not open an office in Belfast.