Letter (alphabet)

You may be looking for the method of correspondence.

There were twenty-six letters in the English language alphabet: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, V, U, W, X, Y and Z. (TV: The Masque of Mandragora, Midnight, Goodbye, Sarah Jane Smith, Shada, AUDIO: Shada, A Death in the Family)

Behind the scenes

Although in the real world, the alphabet goes "A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z", the version shown in the Doctor Who universe has only ever been presented with 'V' before 'U', rather than 'U' before 'V'.