The government would like you to believe that they have relaxed the planning permission laws and to their credit, they have a small bit.
You are now allowed to do a loft conversion in you property, (providing you have the height in the loft), as long as it is within the roof space. What I mean is that if you have a hip roof (one that slopes in from the side), then you would need your loft conversion to start after that roof. This is the reason that you will see a lot of loft conversions with small dormer windows at the back. To be able to take away that sloping roof at the side and build your loft conversion from the outside wall, Then you need planning Permission.
You are allowed to do a single storey rear extension to your property. On the most people do 3 metres at the rear. The government would like to tell you that you can go out 6 metres at the back, with certain restrictions… (A) Only with your neighbours agreement. Yes your neighbour did his extension 5 years ago and he was only allowed 3 metres. He is not annoyed that your extension could come out 6 metres and over shadow his house. Chances of him agreeing are quite thin. (B). Perfect if you live in a detached house with no one around you. But most of us don’t have that privilege. If you live in a terrace house, then be content that you are only getting 3 metres. If you live in a semi, then your chances are a little better, 70 / 30 against, chances are 3 is what you are getting to.
If you would like to so a double storey at the back, then yes you need planning. And if you are luckily enough, or unfortunate enough (depends if you want to renovate), then you need planning for everything you would like to do. Even down to painting the outside of your house
One close to my heart as I found this to my own detriment, when I started out doing renovations for myself.