There are roadworks near the police station in Brixton which means the P4 is on diversion until 6 April.
There's only one stop in Brixton at the moment; it's on Coldharbour Lane. Go up to KFC/Ritzy, turn left and go 30m down road. I think it's usually home to a P5. Next stop is on Shakespeare Road.
It's not well advertised. I only found out from EDF.