The Public Carriage Office (PCO), which regulates and licenses taxis and private hire (commonly known as minicabs) was transferred from the Metropolitan Police to become part of Transport for London in 2000.

They began operating in the 1960s in competition with hackney carriages after a loophole in the law was spotted (although in some areas it is possible to hold a dual hackney/private hire licence).

This is the same body that now regulates London's licensed taxicabs, but minicab drivers do not have to complete The Knowledge, and although they must undergo a small "topographical test" in order to obtain a Private Hire Driver's Licence, they generally rely on satnavs or local knowledge to take them to the pick up and destination.

[6] In the early 19th century cabriolets (cabs for short) replaced the heavier and more cumbersome hackney carriages.

The London taxicab driver is required to be able to decide routes immediately in response to a passenger's request or traffic conditions, rather than stopping to look at a map, relying on satellite navigation or asking a controller by radio.

In all, some 25,000 streets within a six-mile radius of Charing Cross are covered, along with the major arterial routes through the rest of London.

A taxicab-driver must learn these routes, as well as the "points of interest" along and within 1⁄2 mile (0.80 km) of each end of those routes including streets, squares, clubs, hospitals, hotels, theatres, embassies, government and public buildings, railway stations, police stations, courts, diplomatic buildings, important places of worship, cemeteries, crematoria, parks and open spaces, sports and leisure centres, places of learning, restaurants and historic buildings.

Taxi-driver applicants must be 'of good character', meeting strict requirements regarding any criminal record,[13] then first pass a written test which qualifies them to make an "appearance".

For each route, the applicants must recite the names of the roads used, when they cross junctions, use roundabouts, make turns, and what is 'alongside' them at each point.

[14] Knowledge boys/girls and their online learning communities have been the subject of academic research, including a PhD dissertation by Drew Ross at Oxford University.

In the Up Series documentary films, Tony Walker is seen on his motor scooter learning "The Knowledge" before becoming a cab driver.

In the Chas—The Knowledge miniseries, which was a spin-off from the comic book Hellblazer, Chas Chandler's job as a taxi driver is the basis for various plot elements of the series.

The Knowledge, its runs, and to a certain extent the role of the PCO, form the basis for a future religion in Will Self's The Book of Dave.

[20] The Taxi and Private Hire office is the body responsible for licensing taxicabs within Greater London.

The discarded coaches of aristocratic families, complete with their coat of arms, were among the first hackney carriages to ply for hire.

Smaller towns and rural areas allow more varieties of passenger cars, which may require taxis to be painted in a particular livery as a licence condition.

Hartlepool proposed a two-colour scheme with a standard manufacturer colour such as white, silver or black as a base, and retain yellow only on the bonnet and boot, but abandoned plans after a consultation.

[43] Elsewhere there are two types of "taxi"—hackney carriages (licensed under the Town Police Clauses Act 1847), which may pick up fares on the street or be pre-booked and have a meter that charges a rate set by the local authority (alternatively the driver may negotiate a lower fare with the customer), and private hire vehicles (licensed under the Local Government (Miscellaneous Provisions) Act 1976) which must be pre-booked and whose rates are set by the private hire operator.