Tax hidden by the Conservatives (3)

I believe the answer is:

vat

'tax' is the definition.
(British sales tax)

'hidden by the conservatives' is the wordplay.
'hidden' indicates the answer is hidden within the clue.
'VAT' is hidden in the letters of 'by conservatives'.

(Other definitions for vat that I've seen before include "Tank for holding liquids" , "Large barrel" , "Barrel - tax" , "Container for liquids" , "Fermentation vessel" .)

I've seen this clue in the Evening Standard.

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