On 13 March 2019 the UK Government announced temporary rates of customs duty on imports into the UK after a no-deal EU Exit.
The vast majority of seafood lines will be available for import duty free. The remaining tariff lines, amounting to 21 tariff lines, will command tariffs that range from 7.5% to 15% for unprocessed fish and are set at 24% for prepared or preserved tuna.
The UK government announcement also contains information on preferential tariffs on imports from a number of countries, including Chile, the Faroe Islands, and countries that benefit from the General System of Preferences (GSP) scheme.
The official tariff announcement is available through this link, and there is seafood-specific information produced by Seafish available here.