Quote:It's still ridiculous that we should be lumbered with 3 (020 etc), 4 (0121 etc.) and 5 (01200 etc.) digit area codes.
If North America can manage with 3 digits, why could the very-expensive Oftel/Ofcom not manage something like that?
The US uses three-digit area codes and seven digit subscriber numbers. This gives about eight million numbers per area code. In areas running out of numbers, a new area code is allocated covering part or all of the old code geographic area. These are the so-called "overlay" codes. New York has multiple area codes covering the same area. The end result is numbers within the same building having different area codes and a very confusing set of rules as to exactly what you need to dial to connect.
In the UK, subscriber number lengths are adjusted according to population density. Each area code originally covered roughly the same land area (with a number of exceptions in major cities and in the most remote rural areas), so areas with low population density have a longer area code and a shorter subscriber number.
UK telephone numbers originally had three or four digits in rural areas and four or five digits in towns. Over time these numbers have all grown longer. Nowadays it is common to see four, five or six digit subscriber numbers in rural areas, five or six digit subscriber numbers in towns, and seven or eight digit subscriber numbers in cities. Six, seven and eight digit subscriber numbers are the most common.
In order to have a consistent total number length, using longer subscriber numbers means having shorter area codes. Popular formats include 2+8, 3+7, 4+6 and 5+5, with a few places still using the shorter and older 4+5 or 5+4 formats (total length is one digit shorter).
Most towns have 790 000 numbers available (4+6), while a city might have 7 900 000 numbers (3+7). London and several others each have 79 000 000 numbers (2+8).
If the UK had stuck to using four digit area codes and six digit subscriber numbers, London would now have 27 area codes, almost one per borough. Birmingham and Manchester would each have seven area codes. Cardiff, Bristol and Reading would now be on their third area code.
A number of cities have a three digit area code and seven digit subscriber number. These include Glasgow, Bristol, Leicester, Manchester and others. If that system had continued in London, London would now have three area codes and be heading towards starting a fourth.
Instead, London now has a single area code, 020. London has a two digit area code and eight digit subscriber numbers. Northern Ireland uses the same system, but with the 028 area code.
At one time there was a plan to convert the whole country to that 2+8 format. The whole of South-East England would have used the 023 area code, the whole of Scotland perhaps 027, and the Midlands all under 024. There would have been a single area code for South-West England, and another for Northern England. The 029 area code would have covered the whole of Wales.
All that you would have been able to tell from the eight-digit subscriber number within your new area code was that it was somewhere within about 150 to 200 km of wherever you are. Further expansion of that system was abandoned some years ago, but not before Coventry and a few others had been lumbered with it.
The UK has a flexible system built using a (mostly) consistent ten-digit number length. In low population density areas, longer area codes are paired with shorter subscriber numbers. Conversely, in high population density areas, shorter area codes are paired with longer subscriber numbers.
This new system closely matched demand for numbers until Ofcom allowed up to 600 providers to each reserve 10 000 numbers (nowadays 1000 numbers) within each area code - but that's a whole other conversation.
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