Do I need to apply for planning permission, and building regs?

as you are changing the structure(installing a door) building regs will be needed

Check with building control 1.Draw a sketch of the proposed job 2.Write down underneath the sketch a short note of what you've told us here 3.Explain what materials you will use The BCO may ask further questions to which you should answer truthfully The job will be judged by the BCO on it's merits to whether it need Building regs or not Hope this helps

Permission will not be needed, however, you must inform building control, and pay a fee. This type of structures you can erect under loft development.

Possibly, possibly not - difficult to say without seeing the site or drawings, but you will need a party wall agreement with your neighbour if you build on the boundary or if your foundations project under the boundary. Or move the wall inside the line of boundary and then you don't need a party wall agreement.

NO you would not require any planning permission, this would fall under your permitted development due to the size. just do a web search for pd rights see if the description matches your situation . As for building control. it would be classed as a temp.structure same as conservatories and porches and does not require their involvement. i assume the wall you will build would be a single brick, so you do not need a party wall agreement either, you would class this as a garden wall. just discuss with the neighbour what is a suitable height for the wall. from your description all you need is a good builder to construct it. just be careful with the electrics make sure you have breakers as they could get wet.