The principle governing a banker's duty of secrecy originated from which landmark judicial case?

A borrower has three separate loan accounts with a bank: Loan 1 (a personal loan time-barred by the Limitation Act), Loan 2 (a car loan), and Loan 3 (a business loan). The borrower deposits 2 lakhs into his savings account without giving any specific instruction. If the bank wishes to apply this amount to clear the time-barred personal loan, can the bank legally do so?

Which of the following describes a situation where a bank exercises its 'Right of Set-off' against a customer account?