I also just posted on here the thread link is
http://www.udonmap.com/udonthaniforum/british-passport-renewal-t17450.htmlIn basic terms, download the form C1 from here
http://ukinhongkong.fco.gov.uk/en/help-for-british-nationals/passports/passport-formsDownload the notes too they are helpful.
Fill in the form and send it to the Consulate in HK along with a photocopy of your existing passport picture page (not the actual passport) and 2 passport photos one countersigned on the back. For payment you have 2 options, either a bank draft or as I found easier, download a form to give the consulate permission to take the fee from your credit card. The consulate will send your new passport back by DHL if you pay the extra shipping, something like £20, you authorise this on the credit card form
Form for credit card authorisation is here
http://ukinhongkong.fco.gov.uk/en/help-for-british-nationals/passports/feesscroll down and you find the link to download the pdf form.
address for the HK Consulate is
The Passport Section
British Consulate-General
1 Supreme Court Road
Hong Kong
I send my forms etc via EMS through the PO, 450 bht with a tracking number.
Hope this helps.