Puzzle ZCTI 

Workings

Hint
Consonants and vowels (AEIOU) are each worth something.

Answer
12 miles away.

Consonants are worth 2 and vowels (AEIOU) are worth 3.

Double-Checking
York
   3C + 1V = 3 x 2 + 3 = 9
London
   4C + 2V = 4 x 2 + 2 x 3 = 14
Manchester
   7C + 3V = 7 x 2 + 3 x 3 = 23
Leeds
   3C + 2V = 3 x 2 + 2 x 3 = 12