In most cases it should be possible to make a clear decision on whether your project is permitted or not. Remember, your proposal must pass ALL the tests necessary to be classed as permitted development. It is useful to tick off the limits and conditions as you work through them.
You should check with your LPA whether permitted development rights have been withdrawn by what are known as Article 4 directions, and whether other consents, such as listed building consent, are needed. Remember also that many projects will be subject to the building control regime, whether or not planning permission is required.
If your project passes the permitted development tests you do not need to apply for planning permission and you may decide to go ahead with your project. Before starting work we strongly advise that you seek guidance from your local planning authority and building control body, and to seek professional advice where appropriate.