Liberal backed Labour leader's draft law (4)
I believe the answer is:
bill
'draft law' is the definition.
(I've seen this before)
'liberal backed labour leader's' is the wordplay.
'liberal' becomes 'lib'.
'backed' says the letters should be written backwards.
'labour leader' becomes 'l' (the leading letter of 'labour').
'lib' in reverse letter order is 'bil'.
'bil'+'l'='BILL'
(Other definitions for bill that I've seen before include "informing of damage" , "Poster; statement" , "amount owed" , "List of charges" , "The point of anchor?" .)