Hi, I am already in china. Will I need to go back to the UK to complete my working visa?

I think you can apply for it in HK. The documents required for acquiring the work permit includes:
1.Filled Foreigner’s recruitment application form. It can be downloaded from the website of your local labor bureau. You can ask your employer to get one for you.
2.Copy of business license of your employer’s company, code certificate (copy version) and other registered certificates. Your employer provides these documents.
3.Your personal resume including your final academic qualification and full work experiences. It must be printed out in Chinese and stamped with your employer’s company seal.
4.Related qualifications (TESL certificate for example)
5.Copy of your passport.

PS: the required documents vary from place to place. Some places require more documents. Both you and your employer have to prepare the documents according to the labor bureau's requirements.

Hi
This is hedy from shanghai china.
As far as i know you cant get Z at Hongkong from the Sep 2013.
You have to check it.
If you want to get the work Z without comeback to your country,
we can help you.
Thanks