7.30am in the drizzle, waiting for a bus by the side of Rush Common in Brixton. I am watching two large rats as they bound across the wet grass and forage in the litter. It is broad daylight but they are not afraid. Their nut-brown bodies and long tails and darting movements are there for all to see as they zigzag around, bouncing from place to place, occasionally scuttling back to shelter in the hollow of an ivy-covered tree stump.