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Today's route 21, the second service in London to use this route number, started as such on 6 April 1911, as a daily motor-bus route between Newington Green and Old Kent Road (Canal Bridge), replacing the withdrawn horse-bus service 40. By the end of the First World War, the 21 operated between Wood Green (Fishmongers Arms) and Sidcup or Foots Cray. In the 1920s and 1930s, the 21 as well as its sister 20 (later 21A), connected Wood Green and Sidcup, Swanley and Farningham, as well as Brockley Rise. During World War II, in an effort to save on diesel and rubber, the 21 was cut back from Wood Green to Moorgate (Finsbury Square), this section had been duplicated by trolleybus route 641, which used "home grown" Electricity. From the late 1950s onwards, the 21 was gradually reduced, parts of its route hived off to other services for example the eastern end past Lewisham became a new route 321. In 2005, in a period of increased bus use in London, the 21, after a period of 65 years absence, has once again been extended to Newington Green.
