Bring about popular return of disbanded force (5)
I believe the answer is:
incur
'bring about' is the definition.
(as in incurring a punishment)
'popular return of disbanded force' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'return of' is a reversal indicator.
'disbanded force' becomes 'RUC' (Royal Ulster Constabulary, disbanded police force).
'ruc' reversed gives 'cur'.
'in'+'cur'='INCUR'
(Other definitions for incur that I've seen before include "Sustain" , "Lay oneself open to" , "Take on (obligation)" , "Invite, bring about" , "Attract" .)