This is the whole area under the jurisdiction of a control centre, abbreviated to FIR, for airspace extending from the surface to 24,500ft (FL245). At and above FL245 the region is known as an Upper Information Region, abbreviated to UIR. The perimeter of an FIR/UIR is known as the boundary.
United Kingdom airspace consists of two Flight Information Regions, with separation between the two at latitude 55 degrees North. The Scottish Air Traffic Control Centre at Prestwick covers the Scottish region (Scottish FIR) including Northern Ireland, and the London Area and Terminal Control Centre at West Drayton covers England and Wales (London FIR). Southern Ireland is controlled by the Shannon Air Traffic Control Centre. Surrounding UK airspace to the south and east are the regions of other European countries, and to the north and west the ocean areas are controlled by Reykjavik Oceanic Control and Shanwick Oceanic Control respectively.
At Manchester there is an Area Air Traffic Control Centre which deals with traffic below FL175 in the Manchester area.