It seems that unscrupulous / lackadaisical property developers didn't bother to connect a row of town houses in Ealing to the main sewers when they were built ten years ago; Thames Water accidentally discovered that the buildings in Queens Walk were discharging their waste water (laundry, poo, etc) into the surface water drains - that then run into the river Brent. The effluent from fewer than ten houses, diluted with rainwater, won't have caused a huge amount of pollution, but if only it stopped there...
Thames Water reckons as many as one in ten London homes have some kind of misconnection, diverting one and a half Olympic-sized swimming pools worth of waste water through the surface water drains. Apparently a good way to tell is to see whether rainwater pipes are draining into the same gulley as the pipes from your washing machine et al. (Londonist just nipped outside for a look, and has come back in with a concerned look on its face.) As if we didn't have enough to worry about, what with the crumbling Victorian mains and fatbergs.
