Kitchen Plan's to be Drawn Up

Your architect will no doubt have to lodge a Building Control application for the works that show any new/alternations to existing drainage and any ventilation requirements to the new kitchen etc.
Are you having any structural works done eg new steel beams? If so, this should form part of the Architect's Building Regs submission. And if there are any new beams these will need to be sized by a Structural Engineer and their calculations submitted.
Best get the Building Regs Application in early as if there are any additional requirements by the council these can be incorporated into the build.
I agree- unusual to have a percentage based fee for this one.

Zzz!