Tea lady

A tea lady provided tea to the Third Doctor as he worked at his laboratory in UNIT HQ.

As such, she would be one of only a few people allowed to enter the laboratory, in addition to the Brigadier and his personal staff as well as the Doctor himself.

The Doctor briefly mistook Jo Grant for the tea lady when she attempted to introduce herself as his assistant. (TV: Terror of the Autons, COMIC: The Heralds of Destruction)

At some point, took advantage of the tea lady's access to the Doctor's laboratory, having her implant several listening bugs on his behalf. (COMIC: The Heralds of Destruction)