What is the capital of the United Kingdom?

The capital of the United Kingdom is London. It serves as the political, economic, and cultural heart of the country. London houses key government institutions, including the Parliament and the official residence of the Prime Minister, as well as major cultural landmarks such as the British Museum and the Tower of London.

Each of the other cities mentioned—Edinburgh, Cardiff, and Belfast—are capitals of their respective nations within the UK, with Edinburgh being the capital of Scotland, Cardiff the capital of Wales, and Belfast the capital of Northern Ireland. However, when the question refers to the capital of the United Kingdom as a whole, London is the definitive answer because it is designated as such in terms of national governance and significance.