Others can add more detail if you want it (I'm not a NSEA expert) but Swanwick will be responsible for everything in the London FIR that LATCC AREA control does now. (i.e. most of the London FIR Airways system, with the exception of the important bits covered by colleagues at Manchester, and Terminal Control, London).
Oh, and London Information is relocating to Swanwick as well... on the Afternoon of 26th Jan.
Rgds BEX