Losing Tory leader sitting on fence (8)
I believe the answer is:
trailing
'losing' is the definition.
('trailing' can be a synonym of 'losing')
'tory leader sitting on fence' is the wordplay.
'tory leader' becomes 't' (I've seen this in other clues).
'sitting on' is a charade indicator (letters next to each other).
'fence' becomes 'railing' (I've seen this before).
't'+'railing'='TRAILING'
(Other definitions for trailing that I've seen before include "falling behind in race" , "Lagging behind or tracking" , "Following by using marks or scents left behind" , "Pursuing" , "at the back" .)