I suppose I will depend on whether you want to keep your architect close to you throughout your build, im sure there are company's out there who will just do a building regs submission package .
Once we started I only contacted our architect once for technical assistance and that was for a cad drawing of a pair of 30 degree lintels to send to the lintel supplier so they could manufacture them, other than that he would call to see how we were getting on and I called him a few times to ask for trade recommendations ,who would he use for air tests etc .