London's location is the United Kingdom.
Great Britain . Politically , the island is part of the United Kingdom of Great Britain and Northern Ireland , and constitutes most of its territory . Greenwich Mean Time . It is a term commonly used in the United Kingdom and countries of the Commonwealth , including Australia , New Zealand , South Africa , India , Pakistan and Malaysia ; and in many other countries of the eastern hemisphere . London [ ˈlʌndən ] is the capital and most populous city of England and the United Kingdom . Standing on the River Thames in the south east of the island of Great Britain , London has been a major settlement for two millennia . The London Underground ( also known simply as the Underground , or by its nickname the Tube ) is a public rapid transit system serving London and some parts of the adjacent counties of Buckinghamshire , Essex and Hertfordshire in the United Kingdom .