London's location is the United Kingdom.
Greenwich Mean Time . The term `` GMT '' is especially used by bodies connected with the United Kingdom , such as the BBC World Service , the Royal Navy , the Met Office and others particularly in Arab countries , such as the Middle East Broadcasting Centre and OSN . 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 . Its estimated mid-2015 municipal population ( corresponding to Greater London ) was 8,673,713 , the largest of any city in the European Union , and accounting for 12.5 % of the UK population . 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 .