Spanish city force to scrap uniform requirement primarily (4)

I believe the answer is:

vigo

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'spanish city' is the definition.
(Spanish port city)

I cannot understand how the rest of the clue works.

(Other definitions for vigo that I've seen before include "Spanish port" , "Spanish city attacked by Drake in fifteen fifty eight and fifteen eighty nine" , "Port in north-west Spain" .)

I've seen this clue in The Independent.

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