Clerical worker in dock, one dealing in drugs (3-6)

I believe the answer is:

pen-pusher

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'clerical worker' is the definition.
(I've seen this before)

'dock one dealing in drugs' is the wordplay.
'dock' becomes 'pen' (I've seen this in other clues).
'one dealing in drugs' becomes 'pusher' (I am not sure about this - if you are sure you should believe this answer much more).
'pen'+'pusher'='PEN PUSHER'

'in' acts as a link.

Can you help me to learn more?

(Another definition for pen-pusher that I've seen is " Clerical worker with a boring job".)

I've seen this clue in The Telegraph.

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