Commonwealth

The Commonwealth were the nations allied with the United Kingdom.

The Imperial Club was founded for the dispossessed nobility of Europe and the Commonwealth. (PROSE: The Clockwise Man)

Colonel Peter Rathbone claimed to represent the government of George V, Great Britain and the Commonwealth. (AUDIO: Storm Warning)

The Seventh Doctor was suspected of killing Elizabeth II, the Queen of the Commonwealth. (PROSE: Head Games)

The Eleventh Doctor told the Prince of Wales that his mother, the Queen, was busy with matters of the Commonwealth. (HOMEVID: Bad Night)

Behind the scenes

 * The Commonwealth presumably refers to the Commonwealth of Nations, though this phrase has never been used in-story. It also seems to be used as a synonym for the United Kingdom itself.