Your Bank will do it for you, if you pop in to your local branch they will complete a form for you.
You will need to bring along the beneficiary Bank details including the SWIFT code of the HSBC Bank in China, the account number of the payee and their full name, as well as the address of the branch. Then you need to advise them if you want the funds sent in GBP or Yuan.
It will probably cost between �20-30 to send the funds and you also need to tell them if you need an exact amount credited. If you do, they will ensure that any correspondent Bank charges will be debited to your account separately rather then deducting them from the funds being sent.