EastEnders is set in the fictional East London borough of Walford.
Walford is hardly the most affluent place in the world, but sometimes the scriptwriters need the action to take place in an even rougher, more dangerous part of London - and for that they look south.
One current plotline has several scenes set in the South London neighbourhood of Balham. It is portayed as a wasteland of council flats, dark alleys, and menacing gangs:
I lived in Balham for a year not so long ago, and saw more yummy mummies than hoodies. Wikipedia notes: "Property prices have risen as middle class professionals have moved in, causing the district to lose some of the working class feel it had up till the 1990s."
There are plenty of places in South London that make Walford look like Knightsbridge, but Balham isn't one of them.