Swift pint after BBC concert (6)
I believe the answer is:
prompt
'swift' is the definition.
(thesaurus)
'pint after bbc concert' is the wordplay.
'pint' becomes 'pt' (abbreviation).
'after' says to put letters next to each other.
'bbc concert' becomes 'prom' (as in the BBC Proms).
'pt' put after 'prom' is 'PROMPT'.
(Other definitions for prompt that I've seen before include "Reminder" , "Urge - done without delay" , "Cause; on time" , "Whisper lines to forgetful actor" , "Refresh the memory -- on time" .)