Applying for a china visa in the UK for a non UK national

Hi there
I am currently travelling around Europe and travelling to China as part of a tour in Late April 2013 where I will need a visa to enter the country (coming in by train trans mongolian). Can you inform me if I have the information correct that I can apply for it in London at the Application Service Centre and need to complete both the application form and the suplement form? are there any guidance notes on how to complete these forms?