Crossword Genius

What may need tightening in the City possibly or leafy suburbia? (11,4)

Ross

I believe the answer is:

stockbroker belt

'leafy suburbia?' is the definition.
(term for the suburbs of a city)

I can't explain the rest of the clue.

(Other definitions for stockbroker belt that I've seen before include "wealthy area" , "part of Surrey?" , "Affluent residential area" , "Wealthy neighbourhood" , "Prosperous area" .)

I've seen this clue in The Times.
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