020 is the national dialling code for London in the United Kingdom. All subscriber numbers within the area code consist of eight digits and it has capacity for approaching 100 million telephone numbers. The code is used at 170 telephone exchanges in and around Greater London as part of the largest linked numbering scheme in the United Kingdom. In common with all other British area codes the initial '0' is a trunk prefix that is not required when dialling London from abroad.

United Kingdom area code for London
National calling020
International calling+44 20
Active since1 June 1999[notes 1]
Previous code(s)0171, 0181
Earlier code(s)01; 071, 081
Number format020 xxxx xxxx
Approximate coverage of 020 code (red), compared to Greater London boundary (black)

Location of Tristan da Cunha
Area servedBushey Heath
Thames Ditton
Tristan da Cunha
List of United Kingdom codes

The 020 area code fully replaced older area codes for London on 22 April 2000, following multiple telephone number changes during the 1990s.[notes 1]

As is the case for other codes in the UK, the 020 area code may also be used for services without any physical presence in the area, such as private networks or virtual numbering.[1] As one such user is the Foreign and Commonwealth Office Telecommunications Network, provided by Global Crossing, 020 is also one of the dialling codes used for telephone services on the remote South Atlantic island of Tristan da Cunha.[2]