Unclaimed billions brought up to frame politician (3-3)
I believe the answer is:
lib-dem
'politician' is the definition.
(I know that Lib Dem is a type of politician)
'unclaimed billions brought up to frame' is the wordplay.
'to frame' indicates the answer is hidden within the clue (the answer is framed within the clue).
'brought up' says the letters should be written in reverse (in a down clue, letters go up).
'medbil' is hidden in the letters of 'unclaimed billions'.
'medbil' written backwards gives 'LIB-DEM'.
(Other definitions for lib-dem that I've seen before include "Member of a UK political party (abbr)" , "Nick Clegg is one, in short" .)