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' indicates a hidden word.
'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" .)