Instructions to take on 51 English hospital workers (9)
I believe the answer is:
orderlies
'hospital workers' is the definition.
(I've seen this before)
'instructions to take on 51 english' is the wordplay.
'instructions' becomes 'orders' (I've seen this before).
'to take' means one lot of letters goes inside another.
'on' is a charade indicator (letters next to each other).
'ro' becomes 'LI' (roman numeral).
'english' becomes 'E' (abbreviation).
'li' put next to 'e' is 'lie'.
'orders' going around 'lie' is 'ORDERLIES'.
(Other definitions for orderlies that I've seen before include "Servants" , "Soldiers attending superior officers" , "Military or hospital attendants" , "Solderer I join as soldiers who do errands for officers" , "Hospital workers" .)