Boris Johnson imprisoned by Queen -- it altered things (9)
I believe the answer is:
equipment
'things' is the definition.
(thesaurus)
'boris johnson imprisoned by queen it altered' is the wordplay.
'boris johnson' becomes 'pm' (Prime Minister).
'imprisoned by' is an insertion indicator.
'altered' indicates an anagram.
'queen'+'it'='queenit'
'queenit' anagrammed gives 'equient'.
'pm' put within 'equient' is 'EQUIPMENT'.
(Other definitions for equipment that I've seen before include "Set of instruments that perform a service" , "fitting" , "Kit, apparatus" , "Stuff" , "4 [TACKLE]" .)