If you're carrying out home improvements, you may need planning permission.
Most major changes to your home, such as an extension or loft conversion they may need planning permission.
To seek planning permission, you apply to your local planning authority, submitting architectural drawings detailing the improvements or renovations you wish to make.
You can usually expect to receive planning permission within eight weeks.
Even not all building work require planning permission, however most require building control approval. With this you need more detail drawing showing that the work will comply with a set of standard regulations
For more information go to http://www.planningportal.gov.uk/permission/