Certain properties are exempt from Council Tax, the classes of exemption are:

B owned by a charity (time limited) 
D left empty by a person in prison
E left empty by a person receiving care in a hospital or residential home
F a property waiting for probate or letters of admistration.
G empty because occupation is prevented by law 
H left empty for a minister of religion
I left empty by a person receiving care elsewhere
J left empty by a person providing care for someone
K left empty by a student
L a repossessed property
M Student halls of residence
N dwelling occupied by students only
O UK armed forces accommodation
P visiting forces accommodation
Q property left empty by a bankrupt person
R unoccupied caravan pitch or boat mooring
S occupied only by persons under 18
T unoccupied annex
U occupied only by severely mentally impaired persons
V occupied by a diplomat
W occupied annex to an occupied dwelling