An Article 4 Direction is made under the Town and Country Planning Acts, specifically the Town and Country Planning (General Permitted Development) Order 1995. Article 4 (1) directions apply to listed buildings and Article 4 (2) directions to buildings in conservation areas.
See BCC webpage for details of local Article 4 directions.
Article 4 directions do not mean that that the application will automatically be refused. Applications will be considered, as usual, on their merits.