Clandestine pursuit Tories abandoned (13)
I believe the answer is:
surreptitious
'clandestine' is the definition.
(I've seen this before)
'pursuit tories abandoned' is the wordplay.
'abandoned' indicates an anagram.
'pursuit'+'tories'='pursuittories'
'pursuittories' with letters rearranged gives 'SURREPTITIOUS'.
(Other definitions for surreptitious that I've seen before include "Done by stealth" , "Sneaky" , "Covert, clandestine" , "Furtive" , "Sly" .)