The Old Bailey heard Shaikh Khan, 26, targeted the elderly Jack Mautner - who had more than £1m in his account - and changed the account details to ensure he was not sent a statement.
The manager also stole £10,000 from another customer, Lilia Vasilieva, who did not regularly check her account.
The scam was masterminded by Farah Mahmood, 26, and £15,000 of the cash was channeled through the accounts of Ali Bashir, 26.
Judge Stephan Kramer jailed both Khan and Mahmood for 18 months for a conspiracy, which he said: “struck at the heart of the banking system”.
The Judge said Khan has previous convictions for dishonesty but lied on his CV to get a job at the bank’s Oxford Street branch.
He handled more than 500 ‘Premier’ accounts for the bank’s wealthiest clients.
Bashir worked in a T-Mobile shop and had been friends with Khan since their schooldays.
The first transfer of £5000 was made from Ms Vasilieva’s account to Ali’s account on January 13, 2011 followed by another £5000 on 26 January.
Khan accessed the account using a colleague’s ID and recorded the transfer as a ‘face to face’ transaction.
He also changed the address where the statements were to be sent.
On January 26 Khan and a colleague visited Mr Mautner’s home to discuss a legitimate transfer of £50,000.
Judge Kramer said: “This was a deliberately dishonest and targeted fraud.”
Bashir was given a 12-month sentence, suspended for two years.