In which monarch no longer detains old Conservative government minister? (8)
I believe the answer is:
theocrat
'no longer detains old conservative government minister?' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'in which monarch' is the wordplay.
'in' indicates putting letters inside.
'which' becomes 'that' ('that' and 'which' are often synonymous).
'monarch' becomes 'eocr' (I am not sure about this - if you are sure you should believe this answer much more).
'that' enclosing 'eocr' is 'THEOCRAT'.
Can you help me to learn more?
(Other definitions for theocrat that I've seen before include "One involved in government by religious leaders" , "Deified ruler" , "Roman emperor, for example" , "Revered ruler" , "Moses, for example" .)