Farage is manifestly displaying prejudice against senior citizens (6)
I believe the answer is:
ageism
'prejudice against senior citizens' is the definition.
(I've seen this before)
'farage is manifestly displaying' is the wordplay.
'displaying' says the answer is hidden in the clue.
'AGEISM' is hidden within 'farage is manifestly'.
(Other definitions for ageism that I've seen before include "Prejudice in relation to advanced years" , "Form of discrimination" , "Prejudice on grounds of age" , "Unfair treatment" , "Prejudice or bias against old people" .)