Discover Unionist and Republican in Welsh town (7)
I believe the answer is:
unearth
'discover' is the definition.
(thesaurus)
'unionist and republican in welsh town' is the wordplay.
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'and' is a charade indicator (letters next to each other).
'republican' becomes 'r' (abbreviation).
'in' indicates putting letters inside.
'welsh town' becomes 'neath' (I've seen this before).
'r' inserted within 'neath' is 'nearth'.
'u'+'nearth'='UNEARTH'
(Other definitions for unearth that I've seen before include "Bring out of obscurity" , "reveal" , "Dig up for a hunter" , "dredge up" , "Excavate, dig up" .)