[Brian Griffin]

My suggestion:

IRISH MATTERS

The customs services of Republic of Ireland and the UK shall collect and forward appropriate custom revenue for products destined for their counterpart’s territory.

Border security along the border of the Republic of Ireland and Northern Ireland shall be a matter under the control of their national governments, subject to agreements between their national governments.

https://www.freerepublic.com/focus/f-chat/3710348/posts

[Migraine]

Border security along the border of the Republic of Ireland and Northern Ireland shall be a matter under the control of their national governments, subject to agreements between their national governments.

That's the simple issue; and that's the answer. They've got this. But bureaucrats love to complicate simplicity with non-issues with their own special obfuscatory linguistic infections.