Depending on the nature of your particular build, you may not even need planning permission, but if you do, then making sure you fill out the right forms is crucial.
One of the best ways to clarify this is to follow the guidelines on the government’s website, as this can ensure you don’t go too far wrong.
Your local council website should also have a ‘planning’ section where you can find relevant forms and advice.
You can certainly do it yourself, but sometimes, a little help from a specialist town planning consultant is the best way to ensure that the process runs as smoothly as possible.