With leaders of factory leaving, do up plant (7)
I believe the answer is:
flytrap
'plant' is the definition.
'with leaders of factory leaving do up' is the wordplay.
'with' says to put letters next to each other.
'leaders of' indicates taking the first letters.
'do' becomes 'party' (I've seen this in another clue).
'up' is a reversal indicator (in down clue: letters go upwards).
The initial letters of 'factory leaving' is 'fl'.
'party' back-to-front is 'ytrap'.
'fl' next to 'ytrap' is 'FLYTRAP'.
(Other definitions for flytrap that I've seen before include "Venus ...., carnivorous plant" , "Specialised plant" , "that'll take six-footers" .)