Tax I preserve in religious authority (7)
I believe the answer is:
vatican
'religious authority' is the definition.
(I've seen this before)
'tax i preserve' is the wordplay.
'tax' becomes 'vat' (UK Value Added Tax).
'preserve' becomes 'can' (canning is a kind of preserving).
'vat'+'i'+'can'='VATICAN'
'in' is the link.
(Other definitions for vatican that I've seen before include "religious authority" , "See City" , "European state" , "ecclesiastical centre" , "Pope's residence" .)