The longest continuous journey on the Underground is on the Central Line where a journey from West Ruislip to Epping covers just over 34 miles. But the longest journey underground is on the Northern Line: if you travel between Morden and East Finchley, you will travel more than 17 miles underground
The longest distance between stations is on the Metropolitan Line; Chesham is nearly 4 miles from Chalfont & Latimer. The shortest distance is on the Piccadilly Line: Leicester Square and Covent Garden stations being a mere 0.16 miles. With escalators and lifts at each end, it's quicker to walk!
The shortest line on the system is the Waterloo & City which at 1.38 miles easily beats the former holder of the title, the East London Line (five miles) when the former was taken over from British rail in 1994.