London Underground Promo from 1990.

The London Underground is a metro system serving a large part of Greater London and neighbouring areas of Essex, Hertfordshire and Buckinghamshire in the UK. It is the world’s oldest underground railway. It was also the first underground railway to operate electric trains. It is usually referred to as the Underground or the Tube—the latter deriving from the shape of the system’s deep-bore tunnels—although about 55% of the network is above ground.

The earlier lines of the present London Underground network, which were built by various private companies, became part of an integrated transport system (which excluded the main line railways) in 1933 with the creation of the London Passenger Transport Board (LPTB), more commonly known by its shortened name: “London Transport”. The underground network became a single entity when London Underground Limited (LUL) was formed by the UK government in 1985. Since 2003 LUL has been a wholly owned subsidiary of Transport for London (TfL), the statutory corporation responsible for most aspects of the transport system in Greater London, which is run by a board and a commissioner appointed by the Mayor of London.

The Underground has 270 stations and approximately 400 km (250 miles) of track, making it the longest metro system in the world by route length, and one of the most served in terms of stations. In 2007, over one billion passenger journeys were recorded.

The tube map, with its schematic non-geographical layout and colour-coded lines, is considered a design classic, and many other transport maps worldwide have been influenced by it.

History
Railway construction in the United Kingdom began in the early 19th century. By 1854 six separate railway terminals had been built just outside the centre of London: London Bridge, Euston, Paddington, King’s Cross, Bishopsgate and Waterloo. At this point, only Fenchurch Street Station was located in the actual City of London. Traffic congestion in the city and the surrounding areas had increased significantly in this period, partly due to the need for rail travellers to complete their journeys into the city centre by road. The idea of building an underground railway to link the City of London with the mainline terminals had first been proposed in the 1830s, but it was not until the 1850s that the idea was taken seriously as a solution to the traffic congestion problems.

info taken from Wikipedia