Metalworker with his own field in London (5)

I believe the answer is:

smith

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'metalworker' is the definition.
(synonyms)

I don't understand the rest of the clue.

(Other definitions for smith that I've seen before include "Worker in metals" , "Shoemaker" , "Metal worker" , "Common English surname" , "Commonest name" .)

I've seen this clue in the Evening Standard.

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