While the UK was a member of the EU, trade and people moved relatively freely through the UK’s “soft” borders based on EU rules. Now, Brexit supporters argue, the UK can decide who and what gets into the UK by “hardening” the border.
This is a fairly complicated process for the UK’s maritime borders. And it has serious consequences for its only overland border — the one between Northern Ireland and Ireland.
The question of how to regulate the Irish border has caused Brexit-EU negotiations to grind to a halt.