London's location is the United Kingdom.
The British Library is the national library of the United Kingdom and the second largest library in the world by number of items catalogued . 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 . London . London is home to numerous museums , galleries , libraries , sporting events , and other cultural institutions , including the British Museum , National Gallery , Natural History Museum , Tate Modern , British Library , and West End theatres . 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 .