Warning from jobcentre lady when coming back (5)
I believe the answer is:
alert
'warning' is the definition.
(alert is a kind of warning)
'from jobcentre lady when coming back' is the wordplay.
'from' indicates the answer is hidden within the clue.
'coming back' says the letters should be written in reverse.
'trela' can be found hidden inside 'jobcentre lady when'.
'trela' in reverse letter order is 'ALERT'.
(Other definitions for alert that I've seen before include "On the ball" , "Vigilant, watchful" , "Watchful and bright" , "Watchful, quick-thinking" , "Watchful; warning" .)