English papers close to exclusive run down source (5)
I believe the answer is:
eider
'down source' is the definition.
(I've seen this in another clue)
'english papers close to exclusive run' is the wordplay.
'english' becomes 'E' (abbreviation).
'papers' becomes 'ID' (identification papers).
'close to' indicates one should take the final letters (the 'close' to the word).
'run' becomes 'r' (cricket abbreviation).
The final letter of 'exclusive' is 'e'.
'e'+'id'+'e'+'r'='EIDER'
(Other definitions for eider that I've seen before include "Breed of duck" , "Species of duck" , "Reed I turn into a duck" , "Duck with soft feathers" , "Duck valued for its fine soft down" .)