The History

The Black Cabs' history goes back to the time of horse-drawn cabs which were called Hackney Cabs. The term comes from the French word haquenee referring to the ambling horses used to pull the original Hackney Carriages. The Hackney Carriage originated in London, England in 1625. The cabs still come under some of the old rules from the horse-drawn days. The Black Cabs are the only taxis that are allowed to pick people up from the street. There are also mini cabs in London, however they can only collect someone if they have made a prior arrangement by phone.

Before a taxi driver gets his Hackney Cab Licence he or she must pass a test called 'The Knowledge'. This is a difficult test and requires the cabbie to know the streets of central London like the palm of their hand. Mini cab drivers do not need to pass this test.
The Knowledge

Taxi drivers in London undergo a demanding and arduous testing of their knowledge of the city, its daily traffic patterns and the fastest routes between locations. Estimates suggest that gathering the basic understanding needed to acquire The Knowledge involves a full-time year of study, absorbing the information provided by street maps and travelling around the city itself.

The result is that drivers of official London Hackney Cabs are renowned for their detailed and intimate knowledge of London's streets and attractions. Strangely enough, scientific study has shown that possession and expansion of The Knowledge increases the size of the anterior and posterior hippocampi of the brain - the area that handles spatial memory and spatial navigation.

Compared with baseline controls and inexperienced cabbies, long-serving taxi drivers possessed considerable more developed hippocampi.

The Vehicles

There are currently 3 makes of vehicle licensed to ply for hire in London:

LTI (London Taxis International) - FX4 taxi, Fairway taxi, Fairway Driver taxi, TX1 taxi, TX2 Taxi & TX4 taxi.
Metrocab - Series 1 Metrocab, Series 2 Metrocab, Series 3 Metrocab & TTT Metrocab.
Eco City Vehicles - Mercedes Benz Vito Taxi.
All of these vehicles have to conform to the conditions  of fitness as set out by the PCO (Public Carriage Office).
http://www.taxi-london.net/