The most common and most likely answer to this crossword clue is the 16 letter word STOCKBROKERÂ BELT
I've seen this crossword clue in The Guardian
S
T
O
C
K
B
R
O
K
E
R
Â
B
E
L
T
Buddy explains!
The straight part
We know that "Where people are both in and out of capital" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case where people are both in and out of capital = stockbroker belt.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.