Daniel Moss, 24, who worked as a cashier at the bank’s Milford on Sea branch, admitted a series of theft charges at Southampton Crown Court.
Details of how Moss had operated were not revealed due to his guilty plea. The victim suffered from senile dementia and the thefts were perpetrated over a two-month period.
Sentencing was deferred until mid-February but judge Tom Longbotham told Moss he would probably be going to jail. He said: “Clearly this was a substantial breach of trust, given the nature of your employment. A sentence of imprisonment is likely. I want you to be realistic about that and not raise your expectations.”
Moss, who was released on bail, was told there would be a proceeds of crime hearing at a later date at which a list of his assets would be drawn up so money stolen could be repaid.
An HSBC spokesman says: “Daniel Moss was dismissed from our employment last year and no customers have suffered any financial loss as a result of his fraudulent activity.”