Taxicabs are regulated throughout the United Kingdom, but the regulation of taxicabs in London is especially rigorous both with regard to mechanical integrity and driver knowledge. An official report observed that: "Little however is known about the regulation by anyone outside the trade. The Public Carriage Office, 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."

Only licensed hackney carriages can pick up passengers on the street without pre-booking. London's traditional black cabs (so-called, despite being of various colours and advertising designs) are specially constructed vehicles designed to conform to the standards set out in the Conditions of Fitness. London taxi drivers are licensed and must have passed an extensive training course (the Knowledge). Unlike many other cities, the number of taxicab drivers in London is not limited. For many years purpose-designed vehicles were used, but from about 2008 specially-adapted "people carrier" vehicles have also been used.