Businesses have been advised to start making preparations for a no-deal Brexit by acquiring logistics software and consulting customs brokers to assist with any new trading regulations.
Firms that export and import from the EU may also have to apply for licences to continue to do so.
In Northern Ireland, businesses that trade over land with the Republic have been told to contact the Irish government about preparations they may need to make as ministers there have "indicated they would need to discuss arrangements in the event of a no-deal with the European Commission".
The advice forms part of the nine-page "Trading with the EU if there's no Brexit deal" technical notice - one of a raft of documents published by the Brexit department advising businesses and the public on what they need to do to prepare for a no-deal scenario.
The document states: "Businesses should now consider the impacts on them in a no-deal scenario, which would mean a requirement to apply the same customs and excise rules to goods traded with the EU that apply for goods traded outside of the EU, including the requirement to submit customs declarations.
"Businesses should consider whether it is appropriate for them to acquire software and or engage a customs broker, freight forwarder or logistics provider to support them with these new requirements."
The notice adds: "Engaging a customs broker or acquiring the appropriate software and authorisations from HMRC will come at a cost."
On trade in Northern Ireland, the technical paper states that the Government stands ready to "engage constructively" to act in the best interests of the people of Northern Ireland in the event of a no-deal.
However, the department urged businesses in Northern Ireland to contact the Irish government for advice, stating: "The Irish government have indicated they would need to discuss arrangements in the event of a no deal with the European Commission and EU member states.
"We would recommend that, if you trade across the land border you should consider whether you will need advice from the Irish government about preparations you need to make."
The document concludes by stating that the Government "will provide further information on action to take to prepare for this scenario over the coming months".