The leafy south London neighbourhood of Herne Hill is a haven for cyclists who can often be seen lapping the local parks and refuelling at the many cafes that line the suburban streets. But there is something foul in the air of this corner of the capital – and for once it’s not the traffic fumes hitting bicycle riders.

A toxic stench thought to be caused by untreated sewage stuck in Thames Water drains has been emanating from the subterranean depths for months, most likely caused by the summer’s lack of rain.