Make a speech count supporting leader of Opposition (5)
I believe the answer is:
orate
'make a speech' is the definition.
(I've seen this before)
'count supporting leader of opposition' is the wordplay.
'count' becomes 'rate' (I've seen this in other clues).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'leader of' indicates taking the first letters.
The initial letter of 'opposition' is 'o'.
'rate' after 'o' is 'ORATE'.
(Other definitions for orate that I've seen before include "Speechify" , "Deliver a speech" , "Erato (anag.)" , "Lecture" , "Make a flowery speech" .)