What the criteria are under which permitted development rights are allowed.

The Town and Country Planning (General Permitted Development) (Scotland) Order 1992 (the GPDO), grants a general planning permission (or permitted development right) for a variety of developments. These developments are either minor or uncontentious in nature or are required in relation to existing land uses and would be likely to be granted planning permission.
Schedule 1 to the GPDO sets out the 72 different classes of permitted development rights and individual restrictions and conditions on those rights.
Permitted development rights may be restricted in individual cases and a planning application required as a result. For example, most conservation areas, designated under the Planning (Listed Buildings and Conservation Areas) (Scotland) Act 1997, are subject to directions under the GPDO which specify restrictions on classes of permitted development rights particular to the individual conservation area. The Conservation (Natural Habitat, &c.) Regulations 1994 contain restrictions on permitted development rights within designatedNatura Sites where a development would adversely affect the integrity of the site.Also, where a project required environmental impact assessment under the planningprovisions of the Environmental Impact Assessment (Scotland) Regulations1999, then the permitted development rights would not apply and a planning application would be required.