As many as 1000 vehicles cross over each day during January. In an evidence session, business leaders told how problems emerged on the very first ferry arriving in Belfast on January 1 as Brexit took hold - with UK firms unaware of how to comply with new rules. Six of 15 loaded lorries on that vessel were delayed due to incomplete paperwork. There had been no pre-notification about the contents and, on checking the manifest, officials in Belfast found it said only food . Delays of up to 12 hours have held back transit. Customs declarations and, in some cases, additional certification is now required for all goods moving to Northern Ireland from elsewhere in the UK under the terms agreed between London and Brussels.