Onchan District Commissioners must comply with the principles relating to processing personal data, irrespective of whether an entry in the register of controllers and processors is required or not.
The principles can be found in Article 5 of the Applied GDPR and are:
Lawfulness, fairness and transparency
Integrity and confidentiality
There is an overarching principle of accountability, and controllers must be able to demonstrate how they comply with the principles.
Further guidance on the data protection principles is on the Information Commissioners' website.