Cancels orders, action regularly carried out by sergeant (8)
I believe the answer is:
rescinds
'cancels' is the definition.
(to rescind is to cancel or repeal)
'orders action regularly carried out by sergeant' is the wordplay.
'regularly carried out' indicates alternate letters (letters carried out at regular intervals).
'by' means one lot of letters go next to another.
'sergeant' becomes 'DS' (detective sergeant).
'orders'+'action'='ordersaction'
The alternate letters of 'ordersaction' are 'rescin'.
'rescin'+'ds'='RESCINDS'
(Other definitions for rescinds that I've seen before include "Cancels officially" , "Cancels, law or rule" , "Revokes or annuls - discerns accordingly" , "Scraps" , "Countermands" .)