I will be travelling to Hong-Kong with a family of 5. Is

Yes, it may be cheaper to apply from HK. A tourist L type costs HKD$ 360 per person, but if you want to apply for multiple-entry 2-year visa, it may cost more in HK than in UK. However, the price here is for reference only. The final payment is subject to the actual payment given by the consular officers.

Thanks Marcus. Do you know where in HK i can apply for it and how long do they take ? As i will have a total of 8 days to visit both HK and China.
Thanks

You can apply from the Office of the Commissioner of China's Foreign Affairs Ministry. It usually takes four working days. If you only visit Shanghai, Jiangsu, and Zhejiang in mainland, and after 144 hours, you will leave for a country or region rather than HK, I advise you to check whether you are eligible for the free transit policy. If yes, you do not need the entry permit for mainland.

Thank you very much Marcus