|Description:||Includes numbering and trunking arrangements, subscriber line signalling over both physical pairs and V.F. circuits, plus some information about connections for automatic dialing to some Continental European networks.
On the numbering plan, the original allocations for some of the dependent exchanges (real and hypothetical) in the London zone were changed sometime around the late 1960's with the opening of a second zone exchange in London to handle increasing traffic and expansion of numbers within London itself beyond the original 21xxx through 29xxx allocation.
The 81xxx through 87xxx areas were transferred to the new St. Botolph's exchange, which also added 88xxx & 89xxx for London itself.
The original Fleet exchange added 91xxx through 94xxx for London, and saw the remaining dependent areas renumbered, thus:
88xxx Tunbridge Wells -> 95xxx
89xxx Canterbury -> 96xxx
17xxx Norwich -> 97xxx
18xxx Colchester -> 98xxx
19xxx Southend-on-Sea -> 99xxx
Contributed by Paul Coxwell.