The design standards for London taxis are set out in the "Conditions of Fitness", which are now published by Transport for London. The first edition was published in May 1906, by the Public Carriage Office, which was then part of the Metropolitan Police. These regulations set out the conditions under which a taxi may operate and include regulating the taximeter (not compulsory until 1907), the maximum age of the taxi (not more than 15 years), advertisements and the turning circle of . Until the space on the front doors was opened up at the beginning of the 1980s, London Taxis were not allowed to carry any advertisements.