There are only two native species of snake in the UK. They are the Grass Snake (Natrix natrix) & the Adder (Vipera berus). The Smooth snake (Coronella austriaca) - is not a snake, but a legless lizard !
The largest known species of snake on the planet is the Mother Snake that's a tropical snake. It is a huge snake. There were many snakes that were as long as a school bus and as heavy as a car in the prehistoric days.
There are many venomous snake species (about 400 species). Not all have the potency to kill people, though. Some of the more well-known species are... Puff Adder, European Adder, Cobra, Rattlesnake, Taipan & Belcher's Sea Snake.
Australia has about 140 different species of land snake, and 32 known species of water snakes. Of all these species, around 100 are venomous, but the number that could actually inflict a fatal bite number only 12.