“For the GB market, ‘United Kingdom’ is the origin label…”

In “Food labelling: country of origin” published by UK Government, the labelling guidance suggests that:

For the GB market, ‘United Kingdom’ is the origin label for beef and veal from both GB and NI, although additional information may be included if desired. The abbreviation ‘UK’ is permitted. For the NI and EU markets, ‘UK(NI)’ must be used to refer to NI origin.

…

Mixed (GB and NI) origin products must be labelled as ‘UK/UK(NI)’ for sale on the NI and EU market. This labelling is also acceptable on the GB market. If you’re selling on the GB market, mixed (GB and NI) origin products only require ‘UK’, ‘UK’ or ‘UK/UK(NI)’ as their mandatory origin label.

From business compliance perspective, the Made in the UK label is the best solution to indicate origin, while taking geopolitical issue into consideration.