Urchin found British traitor (4)
I believe the answer is:
brat
'urchin' is the definition.
(both can mean a child)
'british traitor' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'traitor' becomes 'rat' (rat can mean a treacherous person).
'b'+'rat'='BRAT'
'found' is the link.
(Other definitions for brat that I've seen before include "child - that's a nuisance" , "A spoiled, badly behaved child" , "Very dry" , "Spoilt child" , "Mervyn -- (Titus Groan)" .)