Tribal conflict involving northern part of UK (8)
I believe the answer is:
clannish
'tribal' is the definition.
(I've seen this before)
'conflict involving northern part of uk' is the wordplay.
'conflict' becomes 'clash' (clashing is a kind of conflicting).
'involving' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'part of uk' becomes 'NI' (Northern Ireland).
'n'+'ni'='nni'
'clash' placed around 'nni' is 'CLANNISH'.
(Other definitions for clannish that I've seen before include "about family" , "Sticking to one group" , "Excluding non-group members" , "Excluding others outside one's own group" , "Tending to exclude those outside the group" .)