One's behind nurse admitting trouble with cocaine (4-3,7)

I believe the answer is:

tail-end charlie

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'one's behind' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'nurse admitting trouble with cocaine' is the wordplay.
'nurse' becomes 'tend' (tend can mean to nurse or look after).
'admitting' indicates putting letters inside (admit can mean to welcome in or accept).
'trouble with' becomes 'ail' (synonyms. I am not sure about the 'with' bit.).
'cocaine' becomes 'charlie' (I've seen this before).
'tend' placed around 'ail' is 'tailend'.
'tailend'+'charlie'='TAIL-END CHARLIE'

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I've seen this clue in The Guardian.

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