A computer disk containing the life insurance details of 370,000 people was lost by the HSBC after they tried to send it to an office in Kent.

The data on the disk was not encrypted, although it was password protected.

The HSBC (Hong Kong and Shanghai Banking Corporation) needed to send the information from its Southampton office to its reinsurer, Swiss Re.

The bank said the data loss was due to the failure of a digital link between Swiss Re, based at Castle House, Castle Hill Avenue, Folkestone, and the HSBC’s Southampton office.

Swiss Re needed the information urgently and the details were put on the disk and sent through the Royal Mail’s business post.

A search failed to turn up the disk, which contains names, life insurance cover levels, dates of birth and whether or not a customer smokes.

A spokesman for the HSBC said that the details were from people nationwide, and not simply people from Folkestone or the South East.

In a statement, the bank added: "The data disk lost by HSBC contains no address or bank account details for any customer and would therefore be of very limited, if any, use to criminals.

"There is nothing else that could in any way compromise a customer and there is no reason to suppose that the disk has fallen into the wrong hands.

"Nonetheless, HSBC would like to apologise to its life assurance customers for any concern this may cause them.

"Each customer will be contacted shortly and a thorough investigation into this matter is underway. The FSA has been informed."