# Number format

*See Sabc.txt for the UK area code list.*

UK telephone numbers use various formats and have a variety of different lengths.

The valid formats and allocations are specified by Ofcom in their codelist.zip file. In the s1_code.txt file they are specified in X+Y format where X is the number of digits in the area code or NDC and Y is the number of digits in the subscriber number.

For geographic numbers the valid formats are 2+8, 3+7, 4+6, 4+5, 5+5 and 5+4 (and 0+10 for NDO numbers).

For all subscriber numbers beginning 2 to 9 within all 01 and 02 area codes the area code is optional to dial when calling from within the same area. In those cases it is common to include the area code in parentheses.

Subscriber numbers beginning 0 or 1 in all 01 and 02 area codes are known as NDO or National Dialling Only numbers. These are always recorded as using 0+10 format but are usually written with a space between the area code and the subscriber number. These numbers are not supposed to be advertised for direct dialling. When the number is dialled the area code must always be included, even when called from another number within the same area code.

For non-geographic numbers the valid formats are 0+10, 0+9 and 0+7. However, for whatever reason known only to Ofcom, they use *10 Digit Numbers* in the s5 and s7 files; a mixture of *10 Digit Numbers*, *10 digit numbers*, *9 Digit Numbers*, *9 digit numbers*, *7 Digit Number* and *7 digit numbers* in the s8 file; and a mixture of *10 Digit Number*, *10 Digit Numbering* and *10 digit numbers* in the s9 file.

The sabc.txt file (also found inside codelist.zip) lists the UK geographic area codes. The official list has many errors, most of which also appear in the National Telephone Numbering Plan document.

### 7 digit NSNs

### 9 digit NSNs

- (016977) 2xxx
- (016977) 3xxx
- (01xxx) xxxxx — click for detailed list
- 0500 xxxxxx
- 0800 xxxxxx

### 10 digit NSNs

- (013873) xxxxx
- (015242) xxxxx
- (015394) xxxxx
- (015395) xxxxx
- (015396) xxxxx
- (016973) xxxxx
- (016974) xxxxx
- (016977) xxxxx
- (017683) xxxxx
- (017684) xxxxx
- (017687) xxxxx
- (019467) xxxxx
- (011x) xxx xxxx
- (01x1) xxx xxxx
- (01xxx) xxxxxx
- (02x) xxxx xxxx — click for detailed list
- 03xx xxx xxxx — click for detailed list
- 055 xxxx xxxx
- 056 xxxx xxxx
- 070 xxxx xxxx
- 07624 xxxxxx
- 076 xxxx xxxx
- 07xxx xxxxxx
- 08xx xxx xxxx — click for detailed list
- 09xx xxx xxxx

### Caveats

01xxx and 01xxxx numbers can have NSN length of 9 or 10 digits. More detailed information can also be found on the 01 numbers page.

0500 numbers always have NSN length of 9 digits.

0800 numbers can have NSN length of 7, 9 or 10 digits.

0845 numbers can have NSN length of 7 or 10 digits.

## See also

- National Telephone Numbering Plan
- Area code
- Charge group
- Trunk code
- 01 numbers
- 02 numbers
- ELNS areas
- Mixed areas
- NSN
- NDC
- NDO
- S-Digit
- F-Digit
- DE block
- 0SABCDEF
- E.123
- Sabc.txt
- (0)
- Regular Expressions for Validating and Formatting GB Telephone Numbers
- Local dialling rules for GB telephone numbers
- Errors in Cisco UK Numbering Plan Documents
- libphonenumber