Criticise former PM causing alarm (6)
I believe the answer is:
dismay
'alarm' is the definition.
('dismay' can be a synonym of 'alarm')
'criticise former pm' is the wordplay.
'criticise' becomes 'dis' (speak disrespectfully).
'former pm' becomes 'may' (Theresa May).
'dis'+'may'='DISMAY'
'causing' acts as a link.
(Other definitions for dismay that I've seen before include "Consternation, discouragement" , "Feeling of surprise and discouragement" , "'Alarm, consternation (6)'" , "Feeling of despair in the face of obstacles" , "Fill with apprehension" .)