The Director CitiesWhen automatic exchanges were introduced in the UK, subscribers in six cities (see table) were given seven digit telephone numbers. These were written as three letters and four digits. One of the most famous was the number for the Metropolitan Police: WHItehall 1212 ie. 944 1212. (See the layout of the UK telephone dial.)The three letters were handled by a piece of equipment called a Director which translated them into the required routing digits to establish the call. So these cities were referred to as the Director Cities. In many cases one physical exchange would handle more than one 'exchange' code. Eg. CROydon, MUNicipal and later 681 and 680 were all served from the exchange in Scarbrook Road. About 1966 the letters were abandoned in favour of all digit numbers because:
The opportunity was taken to re-organise the exchange codes on a geographic basis. In London, the first two digits indicated one of eight switching centres. Using two digits enabled more exchanges to be kept on their original codes. Eg. all 01-68x's were in the South sector. In the other Director Cities the first digit of the exchange code indicated the sector. This meant that there was consistency in that in a full national number the three digits after the zero always gave the charging information and always (with a few local exceptions) gave the routing information. |
The Director Cities
Note how the initial letters of the five cities other than London happened to map neatly on to the middle digits of their codes. Thus Glasgow could have been 0G1. But the codes were never published using letters. Edinburgh was not really large enough to be a Director City but it was included to make the above mapping work! And because it is the capital. The 091 code was created about 1990 for an amalgamation of three charge groups in the North East of England. We could retro-fit the 9 on to Wearside, Washington (County Durham) or tYneside. | ||||||||||||||||||||||||
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Subscriber Trunk DiallingSubscriber Trunk Dialling (STD), known in the USA as Direct Distance Dialing (DDD) was introduced in the UK in the early 1960's. The dialling codes for the non-Director exchanges were written as: zero, two letters with mnemonic significance followed by one, two or three digits. Eg.:
The use of letters was dropped within a few years but in this case there were no actual code changes except that a few codes which had been put on 0Oxx were changed to leave 00 free for other things (eventually International dialling). Eg. 0OX2 Oxford became 0865. |
Roger W. Haworth (sgertrow)
1999 Dec 05 First version
2004 Dec 16 First revision in five years
2016 Mar 13 MyBY closure panick
2018 Jan 05 Link to LDCB68
2022 Dec 02 Bring up to HTML5 standards
