What are (or were) special constables?

Special constables are individuals who carry out limited police duties on a part-time and voluntary basis. Most forces now use special constables. In the past, particularly in the second half of the 19th century and the first half of the 20th century they were used extensively by Scottish police forces in times of emergency, such as wartime and at times when fear of invasion or civil unrest was threatened. Special constables do not receive a police pension, and do not appear in police personnel registers, although separate registers of special constables sometimes survive in police records.