"Proper officer" is the expression used in various pieces of public-health related legislation such as the Public Health (Control of Disease) Act 1984 (and the associated The Public Health (Infectious Diseases) Regulations 1988); and Section 47 of the National Assistance Act 1948.
The Proper officer must be formally appointed by the local authority on whose behalf he or she will act. This may be done by the council, or it may be a delegated power, delegated to an officer of the authority.
Often the Proper officer is a CCDC, acting on behalf of the local authority. Others may have the role of Proper officer, however. For example, for Section 47 of the National Assistance Act, the Proper officer may be a geriatrician, psychogeriatrician, an environmental health officer, or a social worker.