Why go
Their amber TAXI light will be on if they are available. Taxis are required by law to take you wherever you choose (within Greater London) if their TAXI light is on when you hail them. They are a cheap transport option if there are five passengers as they do not charge extras, and many view them as an essential experience for any visitor to London.
The full story
London has two types of taxi: the licensed black cab and the private-hire vehicle commonly called a minicab. Black cabs are the only taxis licensed to ply for hire, while minicabs must be booked through a licensed operator. Black-cab drivers must pass the rigorous Knowledge of central London's streets. Metered black-cab fares reflect distance and time; tipping is optional. Private-hire fares are normally agreed or shown before the journey, and an unbooked vehicle soliciting passengers in the street should not be used. The Knowledge remains a defining part of black-cab licensing and helps distinguish the service from private hire. For either option, use a licensed vehicle and confirm the destination and estimated fare before setting off. This distinction matters most late at night, when unlicensed drivers may approach passengers outside busy venues.