The most common and most likely answer to this crossword clue is the 6 letter word RELIES
I've seen this crossword clue in Financial Times
R
E
L
I
E
S
More clues leading to the result RELIES
Buddy explains!

The straight part
We know that "Banks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case banks = relies.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 RELIES mean?
RELIES verb- (with on or upon, formerly also with in) to trust; to have confidence in; to depend.