Innovatory tax? (3)

I believe the answer is:

vat

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'tax?' is the definition.
(UK Value Added Tax)

'innovatory' is the wordplay.
'VAT' is hidden within the letters.
However, I am uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for vat that I've seen before include "Large tank for liquids, or kind of tax" , "Large barrel" , "Tank for holding liquids" , "Large tank or vessel" , "Liquid storage receptacle" .)

I've seen this clue in the Evening Standard.

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