The telephone area code for London is 020 within the UK, or +44 20 in international format.
If the number is 020 709x xxxx or +44 20 709x xxxx then it is possible to work out the rough area within London if the next digit after 709 is known.
If the number is 070 9xxx xxxx or +44 70 9xxx xxxx then it's a "personal" or "follow me" number that could be terminated anywhere in the world.
(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 entire province of Newfoundland and Labrador is area code 709.
Newfoundland and Labrador in Canada
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.
Area code 020 is London, including the old "inner London" and "outer London" areas.