P

P (Morse code: .--. (TV: The Man Who Never Was)) was the sixteenth letter of the alphabet, following O. (AUDIO: A Death in the Family)

The Seventh Doctor kept a spare TARDIS key hidden in the cubbyhole above the letter "P" in "police box" as seen on the police box-shaped outer plasmic shell of the Doctor's TARDIS. (TV: Doctor Who, AUDIO: The Angel of Scutari)