Tory head's function? In charge of stratagem (6)
I believe the answer is:
tactic
'stratagem' is the definition.
(thesaurus)
'tory head's function? in charge' is the wordplay.
'head's' indicates taking the first letters (I've seen 'head' mean this).
'function?' becomes 'act' (function is a kind of act**).
'in charge' becomes 'ic'.
The initial letter of 'tory' is 't'.
't'+'act'+'ic'='TACTIC'
'of' is the link.
(Other definitions for tactic that I've seen before include "Scheme or ploy used in battle, sport, etc, often within an overall strategy" , "Stratagem, procedure" , "element of strategy" , "Military means to an end" , "Planned action/strategy" .)