Operator not getting on with sudden increase (5)
I believe the answer is:
surge
'sudden increase' is the definition.
(a surge is a sudden increase in something)
'operator not getting on' is the wordplay.
'operator' becomes 'surgeon' (someone who operates).
'not getting' is a deletion indicator.
'surgeon' with 'on' taken away is 'SURGE'.
'with' acts as a link.
(Other definitions for surge that I've seen before include "Rapidly rising water" , "Jerk" , "Outpouring" , "Rise rapidly" , "Sudden rapid rise" .)