Hi Emily, Cockney is a London accent!

There is no such thing as "the" London accent. There are several London accents. By listening to somebody's accent Londoners can immediately figure out which social class somebody is from.

Cockney is a working-class London accent. Upper-class (rich and well educated) London people usually speak a form of Southern RP.  

RP means Received Pronunciation. Unlike other British accents RP is not from any specific town or region. If you speak RP it just means that you have an English accent and you speak correctly, like an educated person, but nobody can tell which region you're from because you don't have a regional accent. You just speak standard English, like news presenters on the BBC.  Actors such as Hugh Grant have RP accents.

@ Oleg

Ya, we're like a mythical story.  Canadian English, Eh!  You've got to get that "Eh!" in there.  We're not advanced like "Americans" in using English.  The British now... I understand Brits!  I was once in Britain for several weeks and, by jove, I didn't need an interpreter. If, however, you visit within earshot of St. Mary-le-Bow Church in East London and someone mentions up the "apples and pears", don't look for a fruit stand.

The United States of America is just south of my home in Canada.  I've travelled through America many times.  But that American English, I tell you!  They've got "huh's", ya'll's in the deep south, miles per hour, Fahrenheit and more.  We have to learn American English to go there.