Back to Basics - What is personal information?

There was a discussion on one of the forums that I belong to about what is considered personal information.

Personal information is any information which relates to a living individual who can be identified -
(a) from that information, or (b) from that information and other information which is in, or is likely to come into the possession of your organisation.

So if you code an account with the reference 123 and in another file link reference 123 with John Smith, then both pieces of information are considered personal information as they can then relate to a living individual.

For example a hairdresser who retains details of their clients, even something simple like a phone and contact number and dates of appointments, are retaining personal information under the Data Protection Act.