Like this chap, Len had to become a composer (6)
I believe the answer is:
handel
'composer' is the definition.
(George Frideric Handel)
'like this chap len had to become a' is the wordplay.
'len had' anagrams to 'HANDEL'.
However, I'm unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for handel that I've seen before include "George Frideric --, composer" , "Sounds as if you could come to grips with this composer" , "German-born composer to the ` `Messiah' '" , "Composer of Messiah, d.1759" , "German composer, George Frederick (1685-1759)" .)