John Nathan-Turner (in-universe)

In January, 1983 in Amsterdam, a man wearing a sheepskin coat walked past the telephone box in which the Fifth Doctor, Tegan Jovanka, and Nyssa stood next to after defeating Omega. (TV: Arc of Infinity)

Behind the scenes
It is believed that the cameo appearance of John Nathan-Turner is nothing more than a blooper, as he had been attempting to manage the crowds during production.

However, Nathan-Turner later claimed that his cameo had been intentional, in the vein of a Hitchcockian cameo.