Great Britain

Note Under the change, the two London areas were reunified under the single (020) code.^[1] New numbers beginning with 7, 8 or (later) 3 were allocated regardless of location.

All of the above areas now have an eight-digit local number, in place of their previous six or seven-digit local number. For a short while, you could use either number for local dialling, but local access to the old, shorter numbers was switched off after a few months of parallel running.

Within London, new 70xx xxxx, 71xx xxxx, 80xx xxxx and 81xx xxxx numbers became available for general use. These began to be allocated anywhere in London, with no regard for the 1990-2000 inner/outer London geographical split.

In all of the other areas, new BC0x xxxx and BC1x xxxx numbers became available for general use at the same time (where 'BC' stands for '76' in Coventry, '20' in Cardiff, etc.).

Northern Ireland

In Northern Ireland, the situation was more complicated. While the primary reason for the changes was the lack of numbering capacity in Belfast (01232), this was not the only reason. When STD codes were introduced in the 1950s, Northern Ireland was allocated only 14 area codes for 34 charging groups. Normal practice in Great Britain was to allocate one area code per charging group but, as calls to Northern Ireland were national rate from anywhere in GB, it was not seen to be necessary to differentiate between all of them. So, area codes covering multiple charge groups ("mixed" areas) were created; in practice this meant that some areas had longer area codes. For example, while Enniskillen was allocated the area code 0365 (0EK5), Kesh was allocated 03656 and Lisnaskea 03657. As a result, numbers in Enniskillen could not begin with 6 or 7, as this would conflict with those of Kesh or Lisnaskea.

All this meant that while Enniskillen's numbers could be six digits long, Kesh's and Lisnaskea's (and those of other dependent exchanges) could only be five digits, due to the 9-digit limit of the length of a phone number at the time. This severely restricted capacity in these areas. As a result, at the Big Number Change, all these dependent exchanges were migrated to different numbers than their parent exchanges; in this instance while Enniskillen's 01365 (the 1 coming from PhONEday) was migrated to 028 66, Kesh went from 013656 to 028 686 and Lisnaskea from 013657 to 028 677. This meant that Kesh could expand into the rest of the 028 68xx range.

Note that the new numbering scheme groups numbers together such that the first digit identifies the county in alphabetical order. The exception is the Greater Belfast area where all numbers begin with 9, regardless of the county. The full list of changes for Northern Ireland^[2] is as in the table above.

National dialling only ranges

In London, old National Dialling Only 0xx xxxx and 1xx xxxx numbers were migrated to new 0axx xxxx and 1axx xxxx numbers (where 'a' is mostly 0 or 1, so far).

In all of the other areas, old National Dialling Only 0xxxxx and 1xxxxx numbers were migrated to new 0aax xxxx and 1aax xxxx numbers.

The migration from old to new numbers was as follows:^[2]

Special services and freephone

The following changes were made to non-geographic numbering ranges to bring them in the 08xx special services range.

The 0500 (Mercury FreeCall) code remained in use after The Big Number Change, but no new numbers were allocated after 28 April 2001. The 0500 range was eventually ceased on 3 June 2017, with numbers transferred to 0808 5xx xxxx equivalents during a three year transition period prior to that date.

The 0800 (BT Freefone) code has remained, but no new nine-digit numbers have been allocated since 1997. Instead, all 0800 numbers issued since that time have ten digits after the leading 0 or +44.

Premium rate

The following changes were made to non-geographic numbering ranges to bring them in the 090x premium rate range.

Personal numbers

Personal numbers moved to the 070 range.

Mobile numbers

The following changes were made to mobile phone numbering ranges to bring them in the 07xxx mobile numbers range.

Pager numbers

The following codes for pager numbers were also changed, so that all are in the 076 range:

Non-standard pager prefixes beginning 01^[3] were moved to their new 076 allocation.

Some of these codes, as indicated by the arrow "→", had already been changed during PhONEday to add a "1" after the initial zero, and now they have been changed again.