The most common and most likely answer to this crossword clue is the 10 letter word GLASSHOUSE
I've seen this crossword clue in The Sunday Telegraph
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Buddy explains!
The straight part
We know that "Unwise place to stow thrones, according to a certain Reverend" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unwise place to stow thrones, according to a certain reverend = glasshouse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GLASSHOUSE mean?
GLASSHOUSE noun- A building made of glass in which plants are grown more rapidly than outside such a building by the action of heat from the sun, this heat being trapped inside by the glass (chiefly commercial).
- A building where glass or glassware is manufactured.
- A military prison.