| Format ; Parent Format ; Comment |
| 20X XXX XXXX ; fixed_2/4/4 ; "Historical London format before it moved to a two-digit area code" |
| 20X XXXX XXX ; fixed_2/4/4 ; "Historical London format before it moved to a two-digit area code" |
| 20 XXXX XX XX ; fixed_2/4/4 ; "Commonly used London format" |
| XXXX XXX XXX ; fixed_4/5-6 |
| XXXX XXX XXX ; mobile_4/6 |
| XXX XXXX XXX ; mobile_4/6 |
| XXX XXXX XXX ; fixed_3/3/4 |
| XXX XXX XXX ; tollfree_3/6 |
| 3XXX XXX XXX ; fixed_3/3/4 ; "UAN numbers beginning with 3 are also often formatted with a 4-digit first group (many search results)" |
