Just a quick post this week to shed some light on the differences between planning permission and building regulations. The short answer is that planning permission is permission to build something (extension, conservatory, etc) but building regulations dictate how it is to be built – types of foundations, insulation, etc.
Using this guidance, you can see that your planning drawings do not have to have too many details on them as to how your proposal will be built, but once planning permission is approved, you may need building regulations drawings which will detail the construction from underground to the roof finish, inside and out.
For more information, see the Planning Portal page here.