When to pay my architect?

Hi,
I've just been furnished with a bill from my architect, albeit the planning application has only just been submitted to the local planning authority. All my friends who have self-built recently have advised that they did not have to pay their architects until the building process was underway? Is it normal practice to have to pay an architect in advance of:
a) Planning being approved
b) Detailed construction drawings being provided?
c) Certifying quality of build for mortgage draw-down?

My concern is the architect gets paid, planning is rejected for whatever reason, further work is required on drawings and I'm held to ransom. Similar concern with respect to obtaining detailed construction drawings for the builder. Are my concerns misplaced?

It is pretty standard to charge a client once the Application has been submitted and registered.
There are normally three stages to the build process - Planning, Working Drawings and Supervision. You pay at the end of each stage for each of those stages. (i.e. what you've been charged now is only c. 1/3 of the amount you will be charged in total)

Our standard practice is to charge 50% of the first phase on registration of the Application and then the other 50% on permission being granted. Perhaps you might suggest this?