Freedom of Information (FoI) and Environmental Information (EIR) legislation provides the public with a right to access information held by a UK public authority, which includes most universities, colleges, or publicly-funded research institutions. See Charlesworth A. & Rusbridge C. (2010) and our Freedom of Information and research data: Questions and answers (via the UK web archive).
The information requested could include your research data, and must be provided unless an exemption or exception allows your institution not to disclose it. A key exemption to FoI legislation is personal data, where the requester is the subject (there is a similar exception under EIR).
If the requester is not the subject of the personal data, the exemptions become more complicated. Always discuss such cases with your FoI practitioner and/or DP practitioner.
In most cases where an FoI exemption applies, it will be an absolute exemption, so no public interest test is needed. The exceptions under EIR are differently worded but similar in effect, although a public interest test may be needed in this case.
FoI requests may also ask for details of ethical approvals for research or details of research data management oversight, including effective compliance with DP obligations.