Hong Kong To Shanghai

I am from the UK and i arrive in Hong Kong on 21st April 2013 and leave to fly to Shanghai on the 25th April 2013.

Whilst I'm aware I do not need a visa to enter Hong Kong, will i need a visa to enter Shanghai. I will be staying until 28th April and then flying home to London , UK.

I understand there is a 72 hour visa you can now get, but i won't have a airplane ticket until i leave Shanghai, only an email confirming my flights. Will this be sufficient or should i get a visa?? 

You need to have confirmed date and seat on your connecting flight. Air carriers are responsible for the transit passengers with no visa that they fly to China. They're also supposed to apply for transit stay on behalf of their passengers. So you should contact your airline so that they can facilitate your transit stay.

Transit stay won't work for someone who plans to fly in, stay, and then book his connecting flight.

Also keep in mind that transit stay applies to situations invovling a third country/region. For example, someone who flies from New York to Shanghai and then back to San Francisco does not qualify for transit stays in Shanghai or Beijing. This is because he's considered traveling from and to the same country/region. Again, your airline should be aware of this.

Passengers in transit are expected to stay in their transit city (Shanghai or Beijing). There do not seem to be practical ways to enforce the particular rule, but that's the law. If you plan to go out of Shanghai while in China, you should get a visa instead of utilizing the visa-free transit. If someone in transit cannot leave within the transit period as planned, the passenger should apply for visa locally.

Good luck.