Key admission by those in a class (6)
I believe the answer is:
gentry
'class' is the definition.
(gentry is a kind of class)
'key admission by' is the wordplay.
'key' becomes 'g' (I've seen this in other clues**).
'admission' becomes 'entry' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'g'+'entry'='GENTRY'
'those in a' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for gentry that I've seen before include "Upper class types" , "(Upper class) people" , "Class of society" , "People of a social position just below the nobility" , "Upper-crust people, just below nobility" .)