This is the standard letter distribution used on Countdown, as supplied by Art Director Demi Sampson in January 2009, and kindly passed on to me by Charlie Reams. Please note that letters are added and removed from time to time by the producers, so this list does not necessarily reflect the letters used in any particular edition of the programme.
A 15
E 21
I 13
O 13
U 5
Total 67
B 2
C 3
D 6
F 2
G 3
H 2
J 1
K 1
L 5
M 4
N 8
P 4
Q 1
R 9
S 9
T 9
V 1
W 1
X 1
Y 1
Z 1
Total 74