Introduction
The first part of this post covered the early years of telephone numbers in the UK, from the first manual exchanges of the early 1900s through to the introduction of UAX in the late 1930s. In this second post, we will look at the introduction of Subscriber Trunk Dialling in 1958 and subsequent large-scale changes to telephone numbers.
Subscriber Trunk Dialling
Initially introduced in 1958, Subscriber Trunk Dialling (STD) allowed subscribers to dial trunk calls without operator assistance. As STD was rolled out, uniform exchange codes, usually called STD codes, were progressively allocated for every exchange in the country. This process took until 1979 to be fully completed.
For uniformity, STD codes all start with ‘0’, so to enable this, the number to call the operator was changed from ‘0’ to ‘100’.
The six large cities that had previously used the Director system were allocated short codes that in general took the form 0x1 (except for London, which had ‘01’), such as ‘021’ for Birmingham and ‘061’ for Manchester.
The first steps of the next big change in UK telephone numbering took place in May 1990, when the ‘01’ code used by London was abandoned and the area covered by it divided between ‘071’ and ‘081’ for central London and outer London respectively.
PhONEday
The change to London numbers in 1990 enabled part of the biggest change to UK telephone numbers in decades that took place on 16th April 1995 (or PhONEday as it was known).
The first change that took place on PhONEday was that 5 new shorter area codes were created for Leeds (0113), Sheffield (0114), Nottingham (0115), Leicester (0116) and Bristol (0117), which were running low on available phone numbers.
The second change is that for all the other area codes the digit ‘1’ was added after the initial ‘0’ of the area codes. So, for example, the two London area codes created in 1990 changed to ‘0171’ and ‘0181’, the code for Liverpool changed to ‘0151’ and the code for Southampton changed from ‘0703’ to ‘01703’.
The purpose of this change was to increase the number of available telephone numbers, by opening up 10 digit numbering series starting with the other now unused digits (2, 7, 8 and 9 etc). These new number series would start to be utilised from 1997 onwards, with new 10-digit mobile, non-geographic and premium-rate services being allocated to ‘07’, ‘08’ and ‘09’ ranges respectively.
Big Number Change
The next big change in the UK telephone dialling plan came in the form of the Big Number Change on 22nd April 2000. In response to the rapid late-90s growth of telecommunications services and the impending exhaustion of local numbers in several cities, a small number of geographic dialling codes were updated to start with ‘02’ and existing 9-digit mobile, non-geographic and premium-rate numbers being converted to 10 digits in 2001.
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