Composer from Southend composed lots (5)
I believe the answer is:
holst
'composer' is the definition.
(Gustav Holst)
'southend composed lots' is the wordplay.
I cannot really understand how this works, but
an anagram of 'lots' is 'olst' which is present in the answer.
A single letter 'h' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'from' acts as a link.
Can you help me to learn more?
(Other definitions for holst that I've seen before include "Scorer" , "Gustav - (The Planets)" , "Gustav --, English composer" , "He scored" , "British composer, 1874-1934" .)