The Customs Union and UK Trade Deals
This brief entry from January 2018 in the Brexit Briefings series makes one point. According to Diane James MEP, if the UK remained in the EU’s customs union, it could not conclude trade agreements of its own, because the union negotiates for all its members.
Her wording was blunt, presenting the claim as a plain fact. Others have noted that the picture is more nuanced, and the question of customs arrangements stayed contested throughout the talks.
Related topics are covered in the Brexit Briefings index.