Format: in text citation
Farming in Sussex during the 1950s was dominated by the landed gentry (Surname, Year).
Format: reference
Author surname, initials. (Year) Title of letter. [letter]. Day Month.
Example: in text citation
Farming in Sussex during the 1950s was dominated by the landed gentry (Williams, 2018).
Example: reference
Williams, B. (2018) My experiences of farming in Sussex during the 1950s. [letter]. 12th July.