On Tue, 3 Apr 2012 19:37:36 +0100, Roland Perry
wrote:

In message , at 19:14:29 on
Tue, 3 Apr 2012, Charles Ellson remarked:
Fixed telephones outwith the "director
areas" (those like Greater London, Glasgow etc. which used the first
three letters of the exchange as the code and where the exchanges used
translation) did not have letters except by accident

I agree that (Inner) London Exchanges had three-letter abbreviations,
but very many provincial exchanges had two-letter abbreviations, plus an
index digit, as a mnemonic...

So Cheltenham was CH2 ( 0-24-2 )
Chichester was CH3 ( 0-24-3 )
Chester was CH4 ( 0-24-4 )
Chelmsford was CH5 ( 0-24-5 ) etc

Not "director areas" though. The style of the STD codes was fairly
deliberate (rather than e.g. a helpful aid for use within the GPO)

The codes I mention above are an example of the ones put in place before
STD, for GPO operators to better remember. They survived into STD
(subscriber) dialling.

Most STD codes were created that way but the majority of telephones
only had numbers on the dials thus actually implementing alpha-numeric
codes would have required all the dials in non-director areas to be
changed as only those in director areas (see below) were intentionally
provided with lettered dials (but being otherwise identical might have
been supplied as a substitute by the Stores Division).

but the future use of letters was dropped before STD working left the
trial stage.

I'm not sure what you are trying to say.

For example, is Chester a "director area"?

No. They were the areas with seven-digit (LLL nnnn) numbers where the
local exchange equipment used translating equipment including
electro-mechanical "directors" to translate the exchange codes into
the actual routing digits (from 1 up to 6) required to reach the
distant exchange and repeat the last four digits to that exchange. The
nominal areas were :-
London
Birmingham
Glasgow
Liverpool
Manchester

Edinburgh was a "pseudo-director" area; AFAIR although the numbering
suggested a director scheme it was actually a non-director area where
the exchanges generally ignored the first digit/letter and used the
two following digits to route the call with the subscriber dialling
the numerical digits direct into the destination exchange (effectively
an early linked numbering scheme).