The real Giacomo Casanova was only thirty at the time of his imprisonment. Frank Finlay was forty-five when he played Casanova, so that he appears in the prison scenes to be looking back, not only over his youth, but the course of his life.
Casanova as an old man is seen working on his memoirs, a few jumbled papers. When finally published in English (in the form that Dennis Potter encountered them, in Willard R. Trask's translation) they ran to 12 volumes.
The music used over the opening and closing credits and in transitions between scenes is the third movement from Antonio Vivaldi's "Autumn".