UK telephone area code 020 (international: +44 20) is London.
The 020 3476 prefix is a "virtual" prefix, meaning that individual numbers may be located anywhere in the greater London 020 zone. No more precise geographic determination is possible.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
The country code and area code of Sniatyn, Ukraine is 380, (8~0)3476.
The country code and area code of Bad Radkersburg, Austria is 43, (0)3476.
The country code and area code of Hettstedt Sachs-Anh, Germany is 49, (0)3476.
This isn't a London code. It is the area code for Brentwood in Essex which is about 30 miles northeast of London.
The country code and area code of East London, South Africa is 27, (0)43.
London is area code 020.
In the UK, area code 020 is London. There is no area code 0208.
Bromley is covered by the area code for London, which is 020.
UK area code 020 is London.
In the UK, there is no area code 0207. Area code 020 is London. Number portability means that it is no longer reliably possible to narrow down a London number to a particular neighbourhood by the first few digits of the number. In fact, the "inner/outer" distinction formerly in the digit 7 or 8 following the area code, no longer holds firm.
The area code for London is 020, or +44 20 from outside the UK.
A UK telephone number like (020) 84xx xxxx will be in London. You need to state two more digits in order to be able to work out which part of London; eg. (020) 8484 or (020) 8411 etc.