Impasse involving British person managed by the same company? (10)
I believe the answer is:
stablemate
'person managed by the same company?' is the definition.
(a stablemate is a colleague)
'impasse involving british' is the wordplay.
'impasse' becomes 'stalemate' (synonyms).
'involving' indicates putting letters inside.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'stalemate' going around 'b' is 'STABLEMATE'.
(Other definitions for stablemate that I've seen before include "person in same outfit" , "Nag" , "companion" , "colleague in same organization" , "Blames Tate (anag) - person from the same club" .)