as far as I read it Eve, Those in tier 3 can't travel out of their area so actually going into tier 3 even visiting I am not sure you could travel back, very complicated
If you can make it fit:
From you.gov "if you live in a tier 2 area, you must continue to follow tier 2 rules when you travel to a tier 1 area. Avoid travel to or overnight stays in tier 3 areas other than where necessary, such as for work, education, youth services, to receive medical treatment, or because of caring responsibilities.You can travel through a tier 3 area as a part of a longer journey"