Can documentation relating to disciplinary warnings be retained after the warnings have expired?

Yes, although there are few good reasons to do so. While the Data Protection Act 1998 does not specifically prevent employers from holding on to such documents, the Information Commissioner's Employment practices data protection code recommends that employers ensure that there are clear procedures in place on how "spent" disciplinary warnings are handled.

One of the data protection principles under the Act is that personal data should not be kept longer than is necessary for the purpose or purposes for which it is being processed. An employer should consider why it is necessary to retain documentation relating to expired warnings indefinitely. As such warnings should not be taken into account in any subsequent disciplinary proceedings, it may be sufficient, and more appropriate, simply to keep a record of the warning instead of all the documentation relating to it. However, if the subject matter is relevant, for example to justify a discrepancy in pay levels, full records should be retained.