As part of your Research Data Management Plan, you would have determined the minimum retention period for your data. Once that period has expired, it doesn’t mean that you automatically have to destroy your data. In fact, it is generally recommended that you retain all your research data for as long as possible without breaching the legal or ethical requirements of your research project. This often means permanent retention.
There are, however, circumstances where you may need to destroy your data. For example, if the Participant Information Statement for your project specifically stated that all research data generated would be destroyed after a certain period of time, you will need to destroy your data accordingly. In this case, the destruction process must be secure and irreversible, and include all your data - both electronic and physical - and include all master copies and any data backups.
The documents linked below provide further information: