Research Services guidance on selecting a lawful basis for research. It isn't possible to link directly to the relevant information, please go to: Lawful - selecting a lawful basis for the processing of personal data
This link is provided as a very clear outline and contrast of the use of consent under GDPR and the common law duty of confidentiality, and is included here for clarification if things are getting confusing. Please use Research Services Guidance in the first instance.
A useful link to the Department of Health guidance on consent under the common law. It is important not to confuse this with consent as a basis for processing under the GDPR. This link is included as a good starting point if things are getting confusing - please check the Research Services advice on this.