'The Old Lady of Threadneedle Street' is the nickname of the Bank of England.
A man, Philip Whitehead, was an employee of this bank and was found guilty of forgery in 1811. He had a sister, Sarah Whitehead, who, upon his execution, suffered a mental breakdown and every day for the next 25 years went to the bank and asked to see her brother. She was buried in what is now the bank's cemetery.

This name is used to refer to the bank and to the woman.