Where in the world?
The flag of the United Kingdom has a blue field with a red cross edged in white superimposed on a diagonal red and white cross.

United Kingdom of Great Britain and Northern Ireland

United Kingdom

Population: 67,215,293

Region: Europe

Subregion: Northern Europe

Capital: London

Top Level Domain: .uk

Currencies: British pound

Border countries

The flag of Ireland has three vertical stripes of green, white, and orange.

Ireland

Population: 4,994,724

Region: Europe

Capital: Dublin