List of telephone exchanges in London

This is a list of telephone exchanges located within Greater London.

Occasionally in areas of high demand two exchanges are located at the same premises, for example Canary Wharf and Poplar.

In earlier times telephone exchanges were given names, such as Euston; a caller would ask the operator for Euston 1234. When dialling was introduced, letters were marked on telephone dials and calls to numbers on the exchange started with the first three letters of the exchange name followed by four digits, as EUS 1234. Letters were then dropped, but dialling remained the same for existing exchanges; "EUS" corresponded to 387, so that the number would be dialled 387 1234. Each GPO exchange had its own three-digit code, so that a 387- number was in the Euston area. The dialling sequence for the same exchange later became 01-387 1234, then 0171-387 1234, and finally 020-7387 1234.

As the telephone system was modernised and liberalised with multiple telephone companies, and numbers became portable the rigid correspondence of numeric codes to exchanges was relaxed, but even today it is likely that a (7)387 number, for example, is located in the Euston area. Lists of numbers allocated to BT exchanges in the UK, including London, are available online, and enable the exchange associated with a given number to be found, if applicable.Locations of exchanges, given a postcode in their catchment area, are also documented.

NOTE: The United Kingdom adopts an open dialling plan for area codes within its public switched telephone network. Therefore, all area codes have a preceding 0 (zero) when dialling from within the United Kingdom. When dialling a UK number from abroad the zero must not be included, but replaced by the calling country's international call prefix followed by the 44, the country code for the UK. Thus a call to the Euston exchange discussed above from the United States would be to 011 (US international prefix) 44 20 (London) 73871234.

The following exchanges are located outside Greater London, but use the London 020 dial code.

London manual exchanges were gradually converted to Director automatic exchanges from 1927. Holborn was the first, at midnight on Saturday 12 November, a local and tandem exchange. Bishopgate and Sloane exchanges followed in six weeks, then Western and Monument exchanges. The London area contained 80 exchanges, and full conversion was to take many years.

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