Dog officer with cock and bull story (6)
I believe the answer is:
collie
'dog' is the definition.
(collie is a kind of dog)
'officer with cock and bull story' is the wordplay.
I cannot really understand how this works, but
'officer' could be 'col' (short for colonel) and 'col' is present in the answer.
'story' could be 'lie' (story can mean a fabrication) and 'lie' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for collie that I've seen before include "See 2" , "Sheepdog with long pointed muzzle" , "Popular sheepdog like Lassie" , "Popular kind of sheepdog" , "Shepherd's dog" .)