Students have a right to confidentiality, both through the Data Protection Act and separately within the Disability Discrimination Act.
A student is not obliged to disclose a disability. However, an institution is expected to take reasonable steps to find out if a student is disabled and what their access requirements are. It is important that an institution creates an atmosphere in which the student feels safe to disclose such information.
Once a student has disclosed their disability, or once an institution might reasonably be expected to know about a student’s status (e.g. if their impairment is visible), there is a responsibility on the institution not to discriminate.
Note also that under the Data Protection Act a student can view and amend their records.
Matters of confidentiality and disclosure are considered further in Encouraging disclosure of a disability.