Just how do you discover new artists when there are so many choices? One solution might be the Saatchi Gallery.
Their website not only acts as a reference point for their own London-based exhibitions and events, but also offers a massive amount of information including links to other art sites.
Their Art and Artist links page connects to a wide range of groups and individuals. It is free to be listed there, making it extremely open and diverse. There is no curatorial restriction here - the only requirement is that listed sites link back to Saatchi.
Take a look at some of the people featured there. You can scroll through the list or sort it by A-Z. It might take a while!