Hearing about British having a partisan mentality (6)
I believe the answer is:
tribal
'having a partisan mentality' is the definition.
(eg favouring a political 'tribe')
'hearing about british' is the wordplay.
'hearing' becomes 'trial' (I've seen this in another clue).
'about' indicates putting letters inside.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'trial' going around 'b' is 'TRIBAL'.
(Other definitions for tribal that I've seen before include "family" , "Characterised by strong group loyalty" , "Relating to a social group" , "concerning clan" , "Like certain social groups" .)