Impasse broken by British person working with me (10)
I believe the answer is:
stablemate
'person working with me' is the definition.
I can't tell whether this definition defines the answer.
'impasse broken by british' is the wordplay.
'impasse' becomes 'stalemate' (synonyms).
'broken by' indicates putting letters inside (inserted letters break into the word).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'stalemate' going around 'b' is 'STABLEMATE'.
Can you help me to learn more?
(Other definitions for stablemate that I've seen before include "Partner" , "One from the same organisation as another" , "One from the same organisation or background" , "colleague in same organization" , "Nag" .)