letters and a number. Outside the director areas, at least three character codes were dialled after an initial '0' which gave trunk access. For example, the code for Bath was BA5, which was dialled as 0225. The rotary dial included the corresponding letters next to the appropriate digits. Problems The continued operation of the system presented a number of problems. As STD was expanded to non-director areas, every telephone which had been issued with no letters on the dials needed to be altered for alphanumeric dialling. With the growth of subscriber dialled international calls from abroad and the incompatible allocation of letters to numbers on foreign dials, there was an increase in the number of dialling errors. In London the number of three letter codes that could be used to represent exchanges had been exhausted. Significant changes were planned to the way calls in and out of the London telephone area were to be handled that required exchange codes to be grouped together into sectors and it was not possible to implement these changes without a transition to all-figure dialling. The General Post Office produced a pamphlet All-Figure Telephone Numbers in 1965 which summarised the problems. Changes From 1966, UK telephone dialling codes ceased to be represented with letters. In most areas this did not require any changes to the telephone codes or numbers, e.g. the Sevenoaks STD code changed from 0SE2 to its numerical equivalent 0732. However, in Director telephone areas such as the London telephone area, the changes permitted many new exchange codes to be issued that did not correspond to letters representing the geographic locations. As '1' was also available for the 'B' and 'C' digits, this allowed many more exchange codes such as 211, 212, 221 to be used. At the same time, many local exchange codes were altered in order to group them into geographic sectors (e.g. GROsvenor became 499 rather than 470) to eliminate the need for all incoming calls to be routed via central London. In the Director areas the old codes continued to work in parallel with new codes until 1970 when the "ANN: All-figure Numbers Now" advertising campaign prompted callers to dial only the new codes. By October 1969 in Edinburgh 79% of calls were being made using the new local exchange codes, in London 72% and in Glasgow 43%. London was the first to withdraw the ability to dial the