People generally need permission before carrying out any form of 'development'. Development means constructing new buildings or significantly changing how land is being used (for example, changing from agricultural use to retail use or buildings changing from an office to a flat)
You submit a planning application for development to your local authority, which will either approve it or refuse it, or approve it with conditions. Your planning application will have a much better chance of gaining approval if you take account of certain things when preparing it.
You can get a clear indication of the local authority's view on an application from the report the planning officer has prepared for the planning committee.
This report will carry a recommendation and must be made available to the public at least three days before the committee is due to sit.
You can usefully get an earlier feel for the report's likely recommendation if you have a good relationship with the planning officers.
They are often prepared to informally discuss the issues and any objections to the application.
It is important to brief them because they might vote to approve an application even if an officer recommends refusal; conversely, they can decide to not endorse the officer's recommendation to approve.
If the planning committee decides to approve an application that could be significant enough to warrant a call-in, what happens next varies among local authorities. In some authorities the decision is passed to a meeting of the full council for formal ratification. If this is the case, you may have breathing space in which to seek a call-in. In any case, try to find out what the procedures are in advance.