Ask anyone to name a great engineer of the Victorian era, and they will probably say Isambard Kingdom Brunel. The little man with the big hat, the big cigar, the big chains, the big railway gauge, the big ships and the big ideas.

So yes, he did quite a lot of big stuff. But far more significant to millions of people was Joseph Bazalgette, one of two heroes who rescued London from death, disease and stinking squalor. London, which was a constant prey to cholera, was little more than one vast sewer, the streets awash and drains leaking into water pipes.

The connection between cholera and contaminated water was established by hero number one, Dr John Snow, who traced an outbreak in 1849 back to a water pump on Broad Street. It turned out a sewer had leaked into the well supplying the pump. What finally prompted serious action was…