Arrived to arrest Unionist draped in old Irish tricolour perhaps as disguise (10)
I believe the answer is:
camouflage
'disguise' is the definition.
(I know that disguise can be written as camouflage)
'arrived to arrest unionist draped in' is the wordplay.
'arrived' becomes 'came' (coming is a kind of arriving).
'to arrest' means one lot of letters goes inside another (arrest can mean capture).
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'draped' becomes 'oflag' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'u' placed inside 'oflag' is 'ouflag'.
'came' placed around 'ouflag' is 'CAMOUFLAGE'.
'old irish tricolour perhaps as' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for camouflage that I've seen before include "Means of disguise" , "Method of blending in fine" , "Green and brown on a green and brown background, say?" , "Disguise (from enemy)" , "blind" .)