Kieran McCarthy: How to start planning a house extension

Confused about when to contact an architect, and if you need a quantity surveyor, and when to contact builders for quotes? 

Kieran McCarthy: "The first thing I would do is consult an architect who will sketch up some draft drawings and comment on any planning permission requirements (if your new extension is to the side of your house you will certainly need planning permission)."

Hi Kieran I’m in a bungalow by the coast considering an extension (living room with mezzanine and maybe an extra bathroom at the back).

I’m wondering where to start... builder or architect first — or do we need an architect, then planning, then building quotes? Is it worth getting a quantity surveyor?