The main planning legislation is the Planning (Northern Ireland) Order 1991 (the "1991 Order"), amended by the Planning (Amendment) Order 2002 and recently further amended by the Planning Reform (Northern Ireland) Order 2006 (the "2006 Order"). This provides that the Department of the Environment for Northern Ireland is the decision maker for planning purposes. There is only an obligation on the Department of the Environment for Northern Ireland in the first instance (working through Planning Service, one of its executive agencies) to consult with the local district council in advance of making a decision.
The Planning (Application of Subordinate Legislation to the Crown) Order (Northern Ireland) 2006 applies the 1991 Order to the Crown in respect of and among other things makes provision for national security, enforcement and preservation of trees.