Authorities are investigating a security breach at Barclays which saw the confidential information of thousands of customers stolen and sold on to unscrupulous City traders.
The bank, police, Financial Conduct Authority and Information Commissioner are all looking into the breach after it was exposed by the Mail on Sunday.
The tabloid says that a whistleblower handed over a memory stick containing details on the earnings, savings, mortgages, health issues and insurance policies of around 2000 Barclays customers.
The information - which also includes passport and national insurance numbers - comes from a stolen database of up to 27,000 files, each around 20 pages long and containing details on customers who had sought financial advice from the bank, the whistleblower claims.
The Mail on Sunday says that the data is "worth millions on the black market" in part because it contains the results of psychometric tests which reveal customers' attitude to risk and could be exploited to talk them into buying "questionable investments".
Some of the 'Barclays leads' ended up in the hands of shady boiler-room operaters, the newspaper said, and from December 2012 to September last year a number of victims were persuaded to buy rare earth metals that did not exist, it is claimed.
Says the whistleblower: "The data is a gold mine for traders because it is so incredibly detailed. It gets them inside the customer's head."
The bank says that the leak seems to have affected customers who used its Barclays Financial Planning business, which was shut in 2011. Regulators have been called in and customers are being contacted.