i am uk citizen in hanoi,can i get a visa for china 30 day single entry

Steven, the visa policy varies on different occasions and different countries. As I know, it is easy to get a single entry China tourist visa in Ho Chi Minh. Your application in Hanoi will be denied if you don't work or reside in Vietnam.

Me and my boyfriend are both English nationals and we had no problem getting our Chinese visa from Hanoi this week. The only issues we had was getting to embassy when it was open (for applications they're open 8.30-11am, I assume Monday to Friday), and because we weren't Vietnamese we had to return the day after applying just to check that it was ok as it isn't automatic for foreigners.
For the visa you need to photocopy both the photo page of your passport and the page with your stuck in Vietnam visa. You also need a passport photo. The forms are there and the people can speak reasonable English. It costs $30 US for 4 days processing, $50 for 2-3 days, and $60 for 1 day.
I hope this helps!