Slither — John Halkin

From his first terrifying, bloody encounter with them Matt Parker knew they were lethal to the human race. Out of the murky sewers they suddenly attacked -- snapping, biting, ripping at his flesh. After the first sensationalism had died down, the newspapers lost interest ... the experts dismissed them as no more dangerous than ferrets ... people started to forget.
But Matt knew different. All the time they were growing in size and numbers -- and they preyed on living flesh!
For when they returned -- slithering out of village ponds, swimming pools, even bath pipes -- the fate of the British population was sealed.

And there was no more horrifying way to die ....