On two occasions, in series 4 and/or 5, Morse uses "Mother" over the radio for the letter 'M', instead of "Mike". This is an especially grievous error, as it is frequently stated in this show (as well as the original Inspector Morse (1987)) that Morse served in the army's signals corps. He would know the phonetic alphabet better than most people.
Given the place and time, Joan, Dorothea, and Shirley should be smoking cigarettes every day.