Cockney's quiet before the Queen's attendant (5)
I believe the answer is:
usher
'attendant' is the definition.
(I've seen this before)
'cockney's quiet before the queen's' is the wordplay.
'cockney's quiet' becomes 'ush' ('hush' - hush is a kind of quiet - said with the 'H' dropped - a cockney accent.).
'before' means one lot of letters go next to another.
'the queen' becomes 'er' (Elizabeth Regina).
'ush'+'er'='USHER'
(Other definitions for usher that I've seen before include "Introduce" , "Escort (to a seat)" , "One puts you in your place" , "may be match participant" , "One who shows people to seats" .)