Colleague in tie drinking a chaser? (10)
I believe the answer is:
stablemate
'colleague' is the definition.
(stablemate can informally mean a colleague)
'tie drinking a chaser?' is the wordplay.
'tie' becomes 'stalemate' (tie in chess).
'drinking' means one lot of letters goes inside another (inserted letters are consumed or drunk).
'a chaser?' becomes 'b' (I can't justify this - if you can you should believe this answer much more).
'stalemate' placed around 'b' is 'STABLEMATE'.
'in' is the link.
(Other definitions for stablemate that I've seen before include "Blames Tate (anag) - person from the same club" , "someone from same place" , "Partner" , "Nag" , "One from the same organisation as another" .)