Article in French newspaper that is socialist (6)
I believe the answer is:
leftie
'socialist' is the definition.
(I've seen this before)
'article in french newspaper that is' is the wordplay.
'article in french' becomes 'le' ('the', the definite article in French).
'newspaper' becomes 'FT' (Financial Times newspaper).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'le'+'ft'+'ie'='LEFTIE'
(Other definitions for leftie that I've seen before include "A radical (colloq.)" , "supporter of "gauche"?" , "socialist" , "Person with radical tendencies (informal)" , "Red" .)