The disk includes the names, dates of birth and life insurance information linked to home mortgages, the Daily Mail reported.

The bank informed Britain's Financial Services Authority of the problem, which could fine the bank if an investigation reveals any mismanagement.

A bank spokesman said the disk "got lost from A to B."

"The reinsurer we sent it to is doing a thorough search for the disk. We will do anything we can to find it," he said.

He also said there were "no financial details" and "no address details" on the disk.

"The possibility of anybody being able to commit fraud ... is quite limited," he said.