The flag of the United Kingdom, is the only flag routinely used on central government buildings in Northern Ireland.
It is an amalgamation of the crosses of
St. Andrew (representing Scotland)
St. George (representing England) and
St. Patrick (representing Ireland).
Coat of Arms
The Coat of Arms for Northern Ireland was replaced by the Coat of Arms for the United Kingdom in 1972.
The Coat of Arms of Northern Ireland was granted to the Government of Northern Ireland in 1924, after the Irish Free State had separated from the United Kingdom. When the Government of Northern Ireland was prorogued in 1972 the arms went out of official use. The grant has not been rescinded, but the arms are considered historical.
The Ulster Banner was the official flag of the Government of Northern Ireland from 1953 to 1972. It is still used to represent Northern Ireland in sporting events in which Northern Ireland competes.