On 13th March 2019 the UK Government published its schedule of tariffs for imports, which is designed to come into force on "exit day" ( currently, 29th March 2019 at 11pm UK time) in the event of a "no deal" Brexit.
The regime is styled "temporary" but there are special provisions outside the regime for the Irish/ Northern Irish border. The Government announcement says that the regime would apply for up to twelve months while a full consultation and review on a permanent approach to tariffs is undertaken.
The announcement states that , under this "temporary" regime, 87% of total imports by value to the UK would be eligible for tariff free access. "Vulnerable industries" would, however, be protected.
As far as the Irish/Northern Irish are border , the temporary tariff regime would not apply but instead trade would continue to flow as freely and as tariff-free as possible into Northern Ireland from the Republic at least for an undefined temporary period , with no checks or controls or goods at the land border between Ireland and Northern Ireland, including no customs requirements for nearly all goods.
Theses measures are unilateral measures on the part of the United Kingdom and have given rise to the criticism ( amongst others) that they are not fully compliant with World Trade Organisation (WTO) rules.
This the stuff of legal argument and lawyers have argued that the UK may be able to get around the legal compliance criticism by relying on the "public morals" exception or the "national security" exception in the General Agreement on Tariffs and Trade 1994(GATT). This is the Agreement which underpins the WTO.
The real point for this Article is that work is clearly being done by the United Kingdom to address the very real problems of a "no deal " Brexit from the Tariffs perspective. The worry, however, is that because the measures are unilateral and would by no means necessarily be matched by similar provisions on the EU side, these unilateral measures would produce a severely distorting effect to trade between the UK and the EU ( and possibly the rest of the World).