UK Citizen on a Tourist Visa currently in Cambodia wants Visa to visit China

1) Do I need to visit the Chinese Embassy in Cambodia (I presume there is only one Embassy - in Phnom
Penh) to get a visa - I presume I can't just complete and print the application form linked to your website
and get it processed at an overland border?

2) If I have to visit, do I have to book a day and time (Ideally Mon 18/06/ - anytime in the morning) or can I
just turn up in the VISA Opening hours?

3) What do I need to bring with me - other than my passport and passport photo's (I have 3) - presumably, it will help if I complete and print off the application form!