A Barclays probe into the leak suggests the data is from 2008 or earlier and is linked to a financial planning unit that was shut in 2011, Carey Withey, a spokeswoman for the company, said in an emailed statement.
Barclays is taking “all necessary steps” to contact the customers affected, she said.
As many as 27,000 client files containing personal and financial information were taken, the Mail on Sunday reported yesterday, citing an unidentified whistleblower.
It is unclear how the files were stolen, the newspaper said, adding the data may be sold to brokers to be used for “investment scams”.
“We are grateful to the Mail on Sunday for bringing this to our attention and we contacted the Information Commission and other regulators on Friday as soon as we were made aware,” Ms Withey said. “This appears to be criminal action and we will co-operate with the authorities on pursuing the perpetrator.”
The UK’s Financial Conduct Authority said it will work with Barclays “to understand exactly what has happened and what steps consumers may need to take,” Lara Joseph, a spokes- woman for the regulator, wrote in an email.
“It’s crucial that people’s personal information is properly looked after,” the UK Information Commissioner’s Office said via an emailed statement.
“We’ll be working with the Mail on Sunday this week to get further details of what has happened here, as well as working with the police.”
A spokesman for the City of London Corporation, which administers the capital’s business district, did not immediately return a call and email request for comment outside normal business hours.
The disclosure of the data leak comes less than a week after chief executive Antony Jenkins turned down his 2013 bonus, acknowledging that regulatory penalties and lawsuits have continued to impose costs on the bank. Regulators are investigating Barclays for possible manipulation of foreign-exchange markets and the bank is reviewing its trading over a “several-year” period, the company said in October.
Barclays is also being probed over whether it properly disclosed £322m (€387m) of payments to Qatar’s sovereign wealth fund as part of a £7bn fundraising during the financial crisis.
The bank was fined £290m for manipulating the London interbank offered rate in 2012, which led to the departure of its then-chief executive Robert Diamond.