From Halopedia, the Halo wiki
The descriptor for people from the area are referred to as British.
In the 18th and 19th-centuries, British colonies began to diverge from Britain itself, in one case leading to war. At some point, the British constructed a training and refueling base on Diego Garcia due to the island's position near India, Pakistan, Hong Kong, and Africa. During World War II, the British managed to crack a German code.
Status as of 26th-century
By the 26th-century, the island of Iona, was part of the North Atlantic Protectorate. As well, the cities of London and Edinburgh were a part of the European Union. Following the Human-Covenant War, a collection of photographs by Jake Courage toured Britain.
Halo 2 and Halo 2: Anniversary
List of appearances