Raise tax -- millions lost in fight about that (7)
I believe the answer is:
elevate
'raise' is the definition.
(I know that raise can be written as elevate)
'tax millions lost in fight about that' is the wordplay.
'tax' becomes 'VAT' (British sales tax).
'millions' becomes 'm' (abbreviation).
'lost in' is a deletion indicator.
'fight' becomes 'melee' (I've seen this in another clue).
'about that' is an insertion indicator.
'melee' with 'm' removed is 'elee'.
'vat' going inside 'elee' is 'ELEVATE'.
(Other definitions for elevate that I've seen before include "Lift to higher place or position" , "Raise, exalt (in rank)" , "To raise in level" , "Raise up, hold aloft" , "Raise or lift" .)