Check claim involving northern dispute (9)
I believe the answer is:
challenge
'dispute' is the definition.
('challenge' can be a synonym of 'dispute')
'check claim involving northern' is the wordplay.
'check' becomes 'ch' (I've seen this in other clues).
'claim' becomes 'allege' (I've seen this before**).
'involving' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'allege' going around 'n' is 'allenge'.
'ch'+'allenge'='CHALLENGE'
(Other definitions for challenge that I've seen before include "tackle" , "Issue an invitation to compete" , "Invite to contest, throw down the gauntlet" , "Disagree!" , "Dispute (a statement)" .)