Of service, but they can go to blazes! (7)

I believe the answer is:

firemen

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'blazes' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Maybe there's a link between them I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for firemen that I've seen before include "Hose wielder" , "They fight conflagrations" , "Their job is to extinguish conflagrations" , "Stokers" .)

I've seen this clue in the Evening Standard.

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