Invented politician accepted by genuine political party (7-2)
I believe the answer is:
trumped-up
'invented' is the definition.
(trumping up is a kind of inventing)
'politician accepted by genuine political party' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'accepted by' indicates putting letters inside (inserted letters are accepted).
'genuine' becomes 'true' (associated in meaning).
'political party' becomes 'DUP' (Democratic Unionist Party).
'mp' put within 'true' is 'trumpe'.
'trumpe'+'dup'='TRUMPED-UP'
(Other definitions for trumped-up that I've seen before include "Concocted with intent to deceive" , "Invented, false" .)