How did we end up with eleven-digit phone numbers in the UK?

It’s often said that travel broadens the mind, and when it’s allowed, it certainly gives you an insight into cultural variances.

For instance, the unseasoned traveller might assume eleven-digit phone numbers are standard throughout the world. Yet that’s not the case.

Countries with smaller populations like Hong Kong and Denmark only use eight digits, though many nations have settled on ten digits.

A few countries have no fixed length for phone numbers, including Germany. This is known as an open numbering plan, and reflects a lack of centralisation in the German phone system.

However, the German system does bear certain similarities with the UK one – including the presence of root numbers. As in many nations, every German phone number starts with zero.

In the UK, almost every phone number is eleven digits long (or ten, if you prefer to ignore the root number when counting).

But how did we end up with this system?

A long time coming

The history of UK phone numbers is a convoluted one, extending to almost 17,000 words on Wikipedia and originating with a diverse history of independent local exchanges.

By the mid-1910s, these had been nationalised under the guidance of the Post Office, which introduced a two-tier system of area codes and individual user numbers.

Smaller exchanges needed fewer numbers, so double or triple-digit local numbers were used in smaller areas compared to four or five-digit subscriber numbers in bigger areas.

By the time the UK’s phone network was reassigned to British Telecommunications in the early 1980s, an eight-digit landline number was the norm.

For instance, dialling 0546 3940 would have connected you to a property in the Argyll village of Lochgilphead. The root was 0, the area code was 546, and local numbers were four digits.

However, this system was struggling to cope with demand.

Exchanges with three or four-digit local numbers were unable to supply new dwellings as available stock was fully used up, necessitating longer local numbers.

Adoption of fax machines and second phone lines compounded matters, as did the burgeoning uptake of mobile phones, which needed to be distinguished from landlines.

Gradually, six-digit local numbers became adopted in most towns, while larger cities like London eventually required seven-digit local numbers.

This was becoming less of an issue as traditional telephones with sluggish self-centring dials gave way to digital push-button units, which could dial out far more quickly.

It’s good to talk

In 1990, London’s 01 STD gave way to inner and outer 071 and 081 codes, doubling the volume of available numbers to 16 million as the capital expanded.

Then in 1995, 1 was inserted after the root number of all geographic area codes, adding an extra digit to every landline number.

This allowed the phone network to expand further by introducing new 02 area codes in 2000.

London transferred over to 0207 and 0208, while the likes of Southampton and Portsmouth received new 023 codes that alleviated pressure on their over-subscribed 01705 network.

The introduction of 02 codes supported future expansion – Northern Ireland now exclusively uses the 028 STD, while the whole of Wales may one day adopt 029 prefixes.

Today, with a few exceptions (such as ten-digit numbers in the Scottish Borders), eleven-digit phone numbers are standard throughout the UK.

With mobile usage increasingly replacing landlines, and some ISPs offering broadband-only services without a working landline, we’re unlikely to need 12-digit numbers any time soon.