It's said to be due to the tea service (4)

I believe the answer is:

duty

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'service' is the definition.
(I've seen this before)

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

(Other definitions for duty that I've seen before include "work you are obliged to do" , "Financial or work obligation" , "Obligation; levy" , "Tariff" , "Moral/legal obligation" .)

I've seen this clue in the Evening Standard.

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