Conservative rebels in periods of political instability? (6)
I believe the answer is:
crises
'periods of political instability?' is the definition.
'conservative rebels' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'rebels' becomes 'rises' ('rise' can be a synonym of 'rebel').
'c'+'rises'='CRISES'
'in' is the link.
(Other definitions for crises that I've seen before include "Times of great danger" , "desperate situations" , "difficult moments" , "Moments of panic" , "moments of disaster" .)