Quality shown by party in charge (7)
I believe the answer is:
calibre
'quality' is the definition.
('calibre' can be a synonym of 'quality')
'party in charge' is the wordplay.
'party' becomes 'lib' (abbreviation for Liberal, uk political party).
'in' is an insertion indicator.
'charge' becomes 'care' ('care' can be a synonym of 'charge'**).
'lib' inserted within 'care' is 'CALIBRE'.
'shown by' is the link.
(Other definitions for calibre that I've seen before include "Diameter of a gun barrel" , "weapon's bore?" , "Personal character" , "Diameter of bullet or shell" , "Ability; barrel diameter" .)