V

V was the twenty-second letter in the alphabet, which, by most accounts, succeeded U and preceded W, (PROSE: The Dalek Dictionary, etc.) however, according to Sarah Jane Smith who recited the alphabet backwards while under mental attack by the Mandragora Helix, she placed V before U. (TV: The Masque of Mandragora)

While binding Chris Cwej's consciousness to the conceptual weapon V-Time, the Surgeon told Cwej that the letter V was, among other things, an ideal representation of the meeting of different points. (PROSE: The V Cwejes)

Behind the scenes
In the real world, V is the twenty-second letter of the alphabet.