Paragraph 8 of Schedule 7 to the Finance Act 2005 (c. 7) introduced, in order to comply with the (then) European Community guidelines on State aid to maritime transport, a general requirement that ships entering the tonnage tax regime in future should be Community-flagged (registered in the European Union (EU) or European Economic Area (EEA)).
Link: The Tonnage Tax (Prescribed and Specified Matters) Regulations 2018
Source: Legislation .gov.uk