Although phone numbers can seem like a long string of random digits, they are actually created using special formats. They help people to identify whether they are calling a mobile, landline or business in the UK. A phone number can also tell you where someone is based if you are able to recognize the area code.

Within the UK, the Office of Communications (Ofcom) is the government-approved regulatory authority that distributes and monitors telephone numbers in the UK. They help distribute phone numbers across the country and generate new numbers when there is a demand.

To help avoid confusion, every phone number in the UK follows a specific format. However, the exact length of each phone number can vary, depending on factors such as the local area code.

In this article, we'll look at the format of phone numbers in the UK and discover what the digits represent. We'll also explore how UK phone numbers have changed in recent years and what changes when you try to call landlines and mobile phones from outside the country.

UK landline phone numbers can have either nine or ten digits after the zero trunk code. The area codes always start with 01 or 02 and can be anywhere between three and six digits long. UK mobile phone numbers have a maximum of 12 digits, including the 07 area code. Non-geographic numbers can start with a two, three or four-digit code that isn't dependent on the physical location of the landline.

You can omit the area code when you dial a UK landline using another landline with the same area code. For example, if you use a Manchester landline to call another Manchester landline, you don't have to dial the 0161 area code at the beginning. However, if you were phoning from anywhere else in the country and wanted to call the same landline number in Manchester, you would need to include the area code.

You must dial the area code if you are phoning a landline using a mobile phone, even if you are within the same geographic area. Mobile phones don't have area codes (except for the country code), which means that you will always have to dial the complete number, no matter where you call from.

How many digits do non-geographic numbers have?

Non-geographic numbers start with prefix codes that are two, three or four digits long. The complete numbers (including the prefix) are usually 11 digits long. Unlike landlines, non-geographic numbers don't have a specific code relating to the area they are based in. This means that you have to dial the complete number, no matter where you are calling from in the country.

The following are non-geographic phone numbers in the UK:

  • 03
  • 05
  • 070/076
  • 080
  • 0845
  • 0870
  • 083/4
  • 0871
  • 09
  • 116
  • 118

Non-geographic numbers are generally used by government agencies and businesses. They may be toll-free, although some numbers cost a small charge to call. Although a non-geographic number won't tell you where it is based, the digits can indicate the type of business or organization that you are phoning. 0800 numbers, for example, are generally used by businesses, while 03 numbers are commonly used by charities and other non-profit organizations.

Landline phone numbers in the UK start with either 01 or 02. Following this, they have a prefix number that is unique to the local geographic area. Villages and small towns usually share the same area code as nearby cities. The area code can be three digits long (such as London's 020 code) or four digits long (such as Edinburgh's 0131 code). However, most cities in the UK have a five-digit area code (such as Bath's 01225 code).

Larger cities in the UK tend to have shorter codes. This is because they are more commonly dialled and designed to be easy to remember. Cities such as London, Manchester and Coventry have three-digit area codes, as does the entirety of Northern Ireland. They may also have an additional digit following that indicates exactly what part of the city the phone line is based.

After the area code, UK landline numbers have a second group of digits. These digits can be six or seven digits long. The majority of landline numbers in the UK have 11 digits in total, although a few have ten digits (including the area code).

You can pay to change your landline or non-geographic number in the UK. Some companies choose vanity numbers to form part of their brand. These are usually easy to remember because they are repetitive or form some kind of pattern. Some individuals also like to keep the same number if they move house.

When written down, there is usually a space separating the landline's area code from the remaining digits. This is so callers can easily identify which area of the country they are calling. For example, a London number would be listed as 020 3424 3601 rather than 02034243601.

Subscriber Trunk Dialling (STD) was introduced so that calls didn't have to be directed through a switchboard. When the system was first introduced in 1958, area codes were assigned to different locations based on the first two letters in the city or town's name. The letters corresponded with the numbered button that each letter shared on rotary dial phones. For example, Aylesbury's original area code was 0296, where 2 represented 'A' and 9 represented 'Y' on rotary phone dials. This was to help individuals identify and remember the area code for various locations.

The system allows long-distance calls within the same country. Trunking groups together sections of the telephone circuit and then branches out to more specific areas. This means that landlines in a local area will share the same prefix and then branch out to different routes depending on the following digits.

Every landline phone in the UK features a zero at the start as the trunk number, followed by either a one or a two. This acts in the same way that a postcode does for physical addresses. The following digits then pinpoint which landline the call needs to be connected to.

Over time, the STD numbers have changed in some areas to accommodate the growing population and increase in phones. Cities can have additional digits tagged onto the end of the location prefix to cover further areas within the local area.

UK area codes were first introduced in 1958 so that individuals could call other people directly rather than using a manual telephone exchange operator. STD numbers were allocated to every area across the UK over the course of 20 years. The volume of STD numbers gradually increased as more people installed landline phones in their homes.

Larger and more prominent cities, such as London, have shorter area codes so that they are easier to identify. Additional digits can also be added to these shorter area codes to identify the landline's location further. For example, London's area code is 020, which includes ranges such as 0207, 0208, 0203 and 0204.

When area codes were first introduced, they usually corresponded with the first two letters of the place name and the buttons on rotary dial phones. However, this trend couldn't be used for every location as the volume of area codes increased. Some area codes, such as London, have also changed on several occasions since STD codes were first introduced.

01 stayed as London's dialling code until 1990 so that the prefix could be used with other area codes. On PhONEday in 1995, the telephone dialling plan in the UK changed and saw the majority of geographic telephone numbers change. In most cases, area codes stayed the same across the country but with an additional number one after the trunk zero. For example, Cardiff's area code changed from 0222 (which corresponded with CA on rotary dials) to 01222.

London's area code changed from 01 to 071 (inner London) and 081 (outer London). This stayed in place until 2000, when the Big Number Change occurred and addressed various dialling issues. Various cities, such as the capital city, Portsmouth and Cardiff were given new area codes. London numbers received 020 as its new area code, which encompassed areas both inside and outside of the capital city.

As the capital city continues to grow, additional digits have been added to the 020 area code to cover more areas. (020) 3 was created in 2005, and (020) 4 was added in 2019.

E.164 is an international system that determines the format of phone numbers around the world. These numbers begin with the country's international access code, followed by the area code and the remaining line numbers. A UK telephone number starts with a +44 country code, followed by the local number or non-geographic number. However, you need to omit the first zero from the area code, as the country code replaces it in the international format.

For example, within the UK, a mobile phone number would look like 07911 123456. However, if you were calling the same number from outside the UK, you would remove the first zero and add +44. This would appear as +44 7911 123456, as the remaining digits stay the same.

UK telephone numbers are usually eleven digits long, although some have ten digits. There are UK area codes assigned to every city, town and village that must be dialled if you are calling from outside of the local area. If you are calling from within the same area, you can omit the area code and simply dial the remaining line numbers. You must dial all the digits when calling a mobile phone from another mobile or a landline.

The UK phone number format starts with the area code, which can be three, four or five digits long. London numbers begin with 020 and are then followed by a further digit which specifies the location further. This is because the capital city has a large volume of landlines that require an increased amount of numbers.

Businesses and organizations tend to use non-geographic phone numbers, which aren't tied to physical locations. These numbers start with prefixes that vary in length. Each prefix indicates the use for the number, such as a competition line, customer inquiries or charity work.