Crossword Genius

Area in which there may be no developments? (5,4)

Ross

I believe the answer is:

green belt

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'area in which there may be no developments?' is the definition.
The definition suggests a singular noun which matches the answer.

'area in which' is the wordplay.
'area' becomes 'green' (green is a kind of area).
'in which' becomes 'belt' (I can't explain this - if you can you should believe this answer much more).
'green'+'belt'='GREEN BELT'

Can you help me to learn more?

(Other definitions for green belt that I've seen before include "Protected land around city" , "Something about London" , "status of karate?" , "land outside city" , "Circle determined to preserve" .)

I've seen this clue in The Telegraph.
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