Please contact the planning section of your local council. Whether the existing garage is portable or not, or if the garage is brick or concrete, the same size or not may all be totally irrellevent if your property and land are covered by any form of permitted development ruling. The only people who can answer this for you properly are the planning dept and everyone else is just guessing which is not what this forum is for. Please see our project on planning permission which is sponsored by the Official Planning Portal.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!