The black London taxi cab is a traditional symbol of London. It looks old-fashioned and clumsy, but in fact it's comfortable and speedy. Besides, London taxi drivers know the city very well. They spend up to two years studying and learning the names of 25.000 streets.
They also must know very well where hospitals, hotels, theatres, clubs, museums, etc. Then they have to pass a very difficult test.
So when you get into the famous black cab you can be absolutely sure that it'll take you wherever you want and by the quickest possible way.