Conservatives backing Starmer's first lies (7)
I believe the answer is:
stories
'lies' is the definition.
(I know this)
'conservatives backing starmer's first' is the wordplay.
'conservatives' becomes 'Tories' (informal term for the Conservative Party).
'backing' is a charade indicator (letters next to each other).
'starmer's first' becomes 's' (1st letter of 'starmer').
'tories' put after 's' is 'STORIES'.
(Other definitions for stories that I've seen before include "See 21" , "House sections" , "Accounts" , "For example, scoops" , "Tales" .)