(Reuters) - Barclays said it had launched an investigation after a newspaper reported that the personal details of 27,000 customers had been stolen and sold, raising the prospect of new fines for the bank.
Confidential information on customers' earnings and health as well as passport details had ended up for sale, The Mail on Sunday reported, citing data provided to it by a whistleblower.
Barclays said it had notified regulators and started an investigation, the initial findings of which suggested the files were linked to the Barclays Financial Planning business which closed in 2011.
"This appears to be criminal action and we will co-operate with the authorities on pursuing the perpetrator," the bank said in a statement on Sunday.
The data leak is a new blow for the British bank after a string of scandals for mis-selling payment protection insurance and manipulating benchmark interest rates, which have resulted in billions of pounds in fines and compensation payouts.
The bank could face new fines should it be found at fault over this data leak.
Britain's data privacy watchdog, the Information Commissioner's Office (ICO), can impose fines of up to 500,000 pounds for serious breaches of the country's data protection rules, while Britain's financial watchdog, The Financial Conduct Authority, has the power to impose unlimited fines.
The ICO said in a statement that it would be working with the newspaper and police to find out what has happened.
The Mail on Sunday said it had been shown 2,000 files on the bank's customers some of which were 20 pages long and containing some of the individuals' attitudes to risk. The whistleblower said there were 25,000 more files on a database.
According to the newspaper, the stolen data is worth millions on the black market because it allows rogue brokers to target people in investment scams.
Barclays thanked the Mail on Sunday for bringing the data leak to its attention.
"Protecting our customers' data is a top priority and we take this issue extremely seriously," Barclays said in its statement.
"We would like to reassure all of our customers that we have taken every practical measure to ensure that personal and financial details remain as safe and secure as possible."
Barclays has been trying to rebuild its reputation after becoming the first bank fined for its part in a global scam to manipulate Libor benchmark interest rates in 2012. The Libor scandal led to the resignation of chief executive Bob Diamond and chairman Marcus Agius.