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No, usually you sort an architect and get you drawings sorted then the builder works from the issued drawings.

This can be possible, but it would be highly dependent on the Building Contractor that is employed, and whether they have an Architect who they can perhaps recommend. However, clients generally prefer to choose an independent Architect, or they contract a Design & Build company that usually provide in house Architectural Services as part of their package.

All architects must be registered with the ARB: http://www.arb.org.uk/public-information/finding-an-architect/ All chartered architects must also be members of the RIBA: https://www.architecture.com/FindAnArchitect/FAAHome.aspx