Except for reduction of contributions (3)

I believe the answer is:

but

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'except for reduction' is the definition.
'but' can be an answer for 'except' (I've seen this before). I'm unsure of the 'for reduction' bit.

'of contributions' is the wordplay.
'of' says the answer is hidden in the clue.
'BUT' can be found hidden inside 'contributions'.

Can you help me to learn more?

(Other definitions for but that I've seen before include "SECOND PART OF 10" , "Only in attribution" , "On the contrary" , "Conjunction meaningn on the other hand" , "Save" .)

I've seen this clue in the Evening Standard.

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