How do I PAY FOR MY TOURIST VISA?

If you are applying for China visa from CVASC in London, if yes, only debit card will be accepted as method of payment for all applications by post. You need fill in the Debit Card Payment Authorization Form and include it in your visa application.
For this form and detailed procedure, you can refer to http://www.visaforchina.org/LON_EN/applybypost/250057.shtml