Further to Jack's post, Potty, also known as "Architectural Consultants", "Architectural Technicians", To give two more examples.
Not trying to do Jack out of a job, but, I've just finished exactly that kind of job for a neighbour. I did the simple design, Building Regs, and Planning Permission myself.
Obviously you wouldn't know how to do that, but you certainly don't need a full blown architect. That's what Architectural Technologists etc are for.