Old Armory became head of local Government (4,5)
I believe the answer is:
lord mayor
'head of local government' is the definition.
The definition suggests a singular noun which matches the answer.
'old armory became' is the wordplay.
'became' indicates an anagram (I've seen 'becoming' mean this).
'old'+'armory'='oldarmory'
'oldarmory' with letters rearranged gives 'LORD MAYOR'.
Can you help me to learn more?
(Other definitions for lord mayor that I've seen before include "VIP in London, perhaps" , "magistrate" , "head for city" , "elected as this?" , "Title of first citizen of a city" .)