I have just looked it up. There are a grand total of three different kinds of snakes in Britain, and the only one I guessed right was the Adder.
Adders, the most famous being the Black, Grass Snakes, Smooth Snakes. There’s also the Slow Worm, which isn’t technically a snake but a lizard with no legs.
Adders are the ones that are venomous; a viking king was once executed by being thrown into a pit full of them), but obviously because of the climate they’re only really active in summer.
I’m joking about the Blackadder of course.