Favouring on account of (3)
I believe the answer is:
for
I believe this is a double definition.
'favouring' is the first definition.
(to be 'for' something is to be in favour of it)
'account of' is the second definition.
(I've seen this in other clues)
'on' is the link.
(Other definitions for for that I've seen before include "and 16 and 20: Notwithstanding" , "On the side of" , "In support of" , "Favouring" , "See 24" .)