London is so well integrated that there's little reason to use a taxi. That's why you have to call to book one, because most people use them for unusual trips,

London is so well integrated that there's little reason to use a taxi. That's why you have to call to book one, because most people use them for unusual trips, such as going to the airport with a lot of luggage, attending an event with formal wear etc. Much cheaper and quicker to use the tube.