Numbers in these five areas are commonly misquoted, e.g. The numbers consist of a two-digit area code matching the pattern 02x, and an eight-digit subscriber number, and this is known as 2 8 format.
The total number of digits is ten, but in a very few areas the total may be nine digits (after the initial zero).
The former Reading area code had already been changed once, by adding a "1" directly after the initial zero as a part of Ph ONEday in 1995. It is used for the third tier of large cities and for Northern Ireland, and was formed as a part of the Big Number Change in 2000.
The new area code is much shorter than the old one, and begins 02 unlike the previous 01 area codes.
Five of these were moved in 1995 as a part of Ph ONEday, with Reading then following a year later.
At the time of the change, an extra digit was added to the subscriber number.
The "area code" is also referred to as an "STD (code)" (subscriber trunk dialling) or a "dialling code" in the UK.