0203

0203 is a geographic telephone area code used in the United Kingdom within the London region. It is part of the London overlay introduced to increase numbering capacity and is assigned to fixed-line numbers alongside existing London codes such as 0207 and 0208. Calls issued from within the UK to a number in the 0203 range are dialed using the local London format, while international callers use the corresponding international format.

The domestic format generally appears as 0203 xxxxxxxx or 0204 xxxxxxxx, with the exact length of the subscriber number varying by block. For example, a typical London landline number in the 0203 range would be dialed as 0203 xxxx xxxx; from outside the local area, you would still dial the full 0203 code to reach the number. Internationally, the country code is +44 and the leading 0 is dropped, giving +44 203 xxxx xxxx.

History and usage: The 0203 code was allocated as part of the UK's London overlay strategy, rolled out in the 2010s to provide additional numbers without changing existing 0207/0208 numbers. It is used by numerous telecommunications providers for new fixed-line services in London, and is not tied to a specific operator. Existing customers with 0207 or 0208 numbers retained their numbers; new assignments began using 0203 or 0204.

See also: List of United Kingdom area codes; Telecommunication numbering plans.