London Buses route 321

This is a list of Transport for London (TfL) contracted bus routes in London, United Kingdom, as well as commercial services that enter the Greater London area (except coaches). Bus services in London are operated by Abellio London, Arriva London, CT Plus, Go-Ahead London, London Sovereign, London United, Metroline, Quality Line, Stagecoach London, Sullivan Buses, Tower Transit and Uno.

TfL-sponsored operators run more than 500 services.

Non TfL-sponsored operators run 36 principal services between parts of Buckinghamshire, Essex, Hertfordshire, Berkshire, Kent, Surrey and Sussex on the one hand and London on the other and one local council sponsored service each in the boroughs of Bexley, Barking and Dagenham and Hackney (extending into Islington).

In Victorian times, passengers could only recognise an omnibus (Latin: for everyone) of an owner and route by the coach's distinctive livery (colour) and line name, with painted signs on the sides showing the two termini to indicate the route. Then, in 1906, George Samuel Dicks of the London Motor Omnibus Company decided that, as the line name 'Vanguard' had proved to be very popular, he would name all lines 'Vanguard' and number the company's five routes 1 through to 5. Other operators soon saw the advantage, in that a unique route number was easier for the travelling public to remember, and so the practice of using route numbers soon spread.

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