All of London is area code 020, or +44 20 in international format, with 8-digit local numbers.
(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.)
City of London with Southwark.
10 Southwark Street London SE1 1TJ
Southwark is a district in London, located on the south bank of the River Thames. In the Canterbury Tales, Southwark is the starting point of the pilgrimage to Canterbury Cathedral that the characters embark on. It serves as a gathering place for the travelers before they set out on their journey.
London Borough of Southwark was created in 1965.
London Bridge connects the City of London with the London Borough of Southwark.
4391EM
most likely to be SE16 5NE
between the City of London and Southwark in London, England
The River Thames
No. The district of Dulwich is in the London Borough of Southwark.
Dulwich is an area of South London in England. Originally Dulwich was entirely in the London Borough of Southwark but as it has expanded it now stretches also into the London Borough of Lambeth.
This isn't a London code. It is the area code for Brentwood in Essex which is about 30 miles northeast of London.