Which London Underground line reaches all nine numbered London fare zones?

The Metropolitan line is the London Underground line that reaches all nine numbered London fare zones. Its outer stations extend through zones 7, 8 and 9 to Amersham and Chesham, while its inner route crosses central London in zone 1.

The line developed from the Metropolitan Railway, which opened between Paddington and Farringdon in 1863. Later extensions carried the railway northwest into the suburbs and beyond the boundary of Greater London.

Most Underground lines operate within a smaller range of zones, although some have stations outside zone 1 and several reach outer zones. The Metropolitan line’s farthest stations are especially notable because Amersham and Chesham are in Buckinghamshire, outside Greater London.