Coming from Eton, all I'm campaigning about is old boy making it as PM (9)
I believe the answer is:
macmillan
'old boy making it as pm' is the definition.
(Harold Macmillan)
'coming from eton all i'm campaigning about' is the wordplay.
'coming from' indicates a hidden word.
'about' shows that the letters should be reversed in order.
'nallimcam' can be found hidden inside 'eton all im campaigning'.
'nallimcam' written backwards gives 'MACMILLAN'.
'is' acts as a link.
(Other definitions for macmillan that I've seen before include "Harold -, former PM" , "Conservative leader" , "PM after Eden" , "Prime Minister" , "Harold -, PM 1957 to 63" .)