The first signs of disruption due to Brexit are being felt by food transporters between Britain and Northern Ireland, with some loads being refused due to confusion over inspection requirements.

Mixed loads of food from several sources are experiencing special difficulties, the BBC reports. The biggest problem is that animal products, including meat, milk and fish, have to be inspected and certified as safe before arriving in Northern Ireland. If a trailer load comes from more than one company, the trailer has to be opened – breaking its seal – and certified, then resealed, often multiple times.

The process has resulted in some haulers refusing to carry mixed loads to Northern Ireland, according to the BBC. One business in Northern Ireland has had nine firms refused to deliver mixed loads of meat from Britain.

The so-called “Irish backstop” was a sticking point in Brexit negotiations, resolved by the last-minute Brexit agreement between the UK and the EU. Since the border between Northern Ireland, which is part of the United Kingdom, and the Republic of Ireland is unsecured, goods arriving in Northern Ireland are subject to European unio regulations.

A government spokesperson told the BBC that goods were "flowing effectively and in normal volumes between Great Britain and Northern Ireland and no disruption has been reported at Northern Ireland ports.”