Ministry of Defence to get 'non-clerical' if Foreign Office to retire bureaucrats (11)
I believe the answer is:
officialdom
'bureaucrats' is the definition.
'ministry of defence to get non-clerical if foreign office to retire' is the wordplay.
'ministry of defence' becomes 'MOD' (abbreviation).
'to get' means one lot of letters go next to another.
'non-clerical' becomes 'laic' (laic means of the laity as opposed to the clergy).
'foreign office' becomes 'FO' (abbreviation).
'to retire' says the letters should be written backwards (retire can mean to go back).
'mod'+'laic'+'if'+'fo'='modlaiciffo'
'modlaiciffo' written backwards gives 'OFFICIALDOM'.
(Other definitions for officialdom that I've seen before include "Bureaucracy" , "Authority" , "mandarins" .)