Proceed (2,5)
(Other definitions for go ahead that I've seen before include "Pioneering (green light?)" , "Permission to proceed" , "Signal to proceed" , "Lead" , "Up-and-coming -- authorisation" .)
'proceed' is the definition.
(synonyms)
This is all the clue.
(Other definitions for continue that I've seen before include "Last" , "Persist" , "Proceed" , "Carry on" , "Don't stop, keep going" .)