The claim: Boris Johnson said goods entering Northern Ireland from Great Britain would only be checked if they are expected to be moved onwards into the Republic of Ireland. He told Sky News "the only checks that there would be, would be if something was coming from GB via Northern Ireland and was going on to the Republic, then there might be checks at the border into Northern Ireland".
Reality Check verdict: Some goods entering Northern Ireland from Great Britain will have to be checked even if they are staying in Northern Ireland.
The Brexit Withdrawal Agreement signed in October means that Northern Ireland will remain part of a "single regulatory zone" with the Republic of Ireland, a zone that will apply EU rules.
A Treasury document leaked a few days ago suggested this would mean new checks on goods being traded between Great Britain and Northern Ireland.
For example, the EU has particularly strict rules on importing "products of animal origin" - that is to say meat, fish and dairy products.
Those products must enter the EU through a border inspection post where all shipments are subject to document checks and a high proportion are physically checked.
Products of animal origin from Great Britain entering Northern Ireland would be subject to these checks whether they are destined to remain there or be moved to the Republic of Ireland.
The island of Ireland is already a single regulatory zone for animal health.
This means that all livestock entering Northern Ireland from GB is currently checked at the point of entry.
A few countries, such as New Zealand, have a deal with the EU where only 1% of consignments of meat and dairy product are checked.
It is possible that the UK could negotiate a similar deal but it would not be able to get rid of checks entirely unless the whole of the UK was going to stay in the single market.
The current political declaration, which sets out the broad shape of the future EU-UK relationship, suggests that is unlikely .