"Lulu" composer Berg (5)
I believe the answer is:
alban
'lulu composer berg' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alban that I've seen before include "First Christian martyr in England" , "-- Berg, composer" , "early martyr" , "Saint who was first British Christian martyr" , "First English Christian martyr" .)