I am traveling to hong kong for 8 days i have a british passport do i need a visa?

Hong Kong has its own entry and exit regulations separate from mainland china (and its own government). 90 or 180 days is allowed based on type of citizenship:

Visa required, except for Passengers with a British passport
with nationality British Citizen for a maximum stay of 180
days.
Visa required, except for Passengers with a British passport
with nationality British Subject , British Overseas
Territories Citizen , British National (Overseas) , British
Overseas Citizen or British Protected Person for a maximum
stay of 90 days.

Hi,

If you are traveling to Hong Kong and you are British Citizen than you do not required Visa.

However if you are planning to visit China from there, than China Visa is required.