The most common and most likely answer to this crossword clue is the 6 letter word SHROFF
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More clues leading to the result SHROFF
Buddy explains!

The straight part
We know that "Banker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case banker = shroff.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 SHROFF mean?
SHROFF noun- A provider of financial services, especially a small-scale independent banker or money changer or a local expert at detecting bad coin.
- A cashier, especially for a carpark.
- Short for shroff office: the office of a shroff at a carpark, etc.
- To act as a shroff, especially to inspect coins to detect debasement, counterfeits, clipping, etc. for a commission.