Information contained in routine medical records, disease registries, completed trials, and research programmes is an invaluable resource for research into public health. The secondary use of such data, which were often collected for unrelated purposes, has demonstrated the late effects of treatment, indicated social differences in health care, suggested environmental causes of cancer, and identified epidemics. For years the United Kingdom has been in the forefront of this research, and the NHS has been a unique source of such data.

In most medical research, doctors and investigators have direct contact with patients and can seek spoken and written consent directly. But research reusing previously collected data may encounter considerable difficulties with respect to both consent and anonymity. The study populations may comprise many thousands of people; some patients will have moved or died; the information may need to be linked to two or more databases; and individual identification may be necessary to prevent double counting. Problems may arise regarding the necessity and practicability of obtaining consent, the degree to which the data can be anonymised without losing vital information, and the security of the data …