The Central Line is the longest single line, at 46 miles. It is also the line with the greatest number of passenger jorneys, 260 million and change, over the 2011/2012 year.
The London Underground did give the East London line to the London Overground to ease its traffic.
On the London Underground map, the Circle Line is coloured yellow.
Central Line
london
The Circle Line Unfortunately this answer is wrong! According to Transport for London the only tube line to connect all London Underground lines is the Jubilee Line.
You need to get the Northern Line to Leicester Square and then the Piccadilly Line to London Waterloo.
Hammersmith and City.
Jubilee Line.
It's on the BAKERLOO Line.
Hammersmith & City line
Black.
Green is the District Line