Vietnamese citizen Applying for HK Visa by mail or in London directly.

Dear,

I'm studying in the UK and would like to travel to HK in 13th September. In order to shorten the processing time, I want to send the application directly to HK however I'm quite confused with the process compared to applying at the Chinese Embassy in London. If I send all the documents fax along with the original application and photo by post, how will I get the visa label affixed to my passport? Will it be better to apply here at Chinese Embassy in London or send it to HK? My course will finish by September, do I still need to ask for the confirmation letter from school?

Many thanks
Jane