Travel Visa one entry for Shanghai and Hong Kong

I go to Shanghai in July 2012 i have a 1 entry visa to China as a UK passport holder , whilst i am in Shanghai i want to fly to hong kong for 3 days , do i need another visa is this permitted on a 1 entry visa?

You'll need another visa to re-enter China. Your one-entry visa will be used for your visit of Shanghai. Hong Kong is visa-free for most visitors but when you travel from Hong Kong to Shanghai, you'll be re-entering Mainland China, which requires visa. And UK does not seem to be on the list of the countries whose citizens can transit through Shanghai visa-free to stay in the city for up to 48 hours.