HSBC has lost a computer disc containing details of 370,000 customers.
The disc - lost whilst being couriered between offices four weeks ago – contained details including names, dates of birth, levels of insurance cover, and whether or not a customer smokes.
HSBC said the disc would have very limited use to criminals.
"The data disc lost by HSBC contains no address or bank account details," saida spokeswoman.
"Nonetheless, HSBC would like to apologise to its life assurance customers for any concern this may cause them."
The bank will contact every customer effected, and has informed the Financial Services Authority (FSA).
The bank still hopes to find the disc, which was password protected.
HSBC is the latest in a line of banks to lose information, with Nationwide and Norwich Union suffering fines from the FSA for losing customer details.
