Worker admits messing around in job (10)
I believe the answer is:
assignment
'job' is the definition.
(I've seen this before)
'worker admits messing around' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'admits' is an insertion indicator.
'around' indicates anagramming the letters.
'messing' with letters rearranged gives 'ssignme'.
'ant' going around 'ssignme' is 'ASSIGNMENT'.
'in' acts as a link.
(Other definitions for assignment that I've seen before include "Task, piece of work" , "job" , "Task or duty" , "Duty to be done" .)