Skilled worker sends a porter mad (12)

I believe the answer is:

tradesperson

'skilled worker' is the definition.

'sends a porter mad' is the wordplay.
'mad' is an anagram indicator.
'sends'+'a'+'porter'='sendsaporter'
'sendsaporter' with letters rearranged gives 'TRADESPERSON'.

I've seen this clue in The Times.

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