The failure to obtain planning permission or comply with the details of a permission is commonly known as a 'planning breach'.
A planning breach usually occurs when:
- A development that requires planning permission is undertaken without the permission being granted - either because the planning application was refused or was never applied for
- A development that has been given permission subject to conditions breaks one or more of those conditions.
A planning breach in itself is not illegal and the council will often permit a retrospective application where planning permission has not been sought.
However, if the breach involves a previously rejected development (or the retrospective application fails) the council can issue an enforcement notice requiring you to put things back as they were.
Your local planning authority can serve an enforcement notice on you when they consider you have broken planning control rules. Normally this will be because they consider what you are doing, or have done, is harmful to your neighbourhood.
The decisive issue for the local planning authority should be whether the breach would unacceptably affect public amenity or the existing use of land and buildings meriting protection in the public interest.
It is illegal to disobey a enforcement notice unless it is successfully appealed against. You can appeal against both refusals of permission and enforcement notices but if the verdict comes out against you and you still refuse to comply you may be prosecuted.