When I were a little lad my mates and I frequently played on the railway embankment alongside our estate. The area swarmed or slithered with them. One day a very alarmed compadre let out a shriek and screamed Anaconda. Eat your heart out Mr Bolt. Us kids hurdled 6' chain link fences and ran 500mts when you were still on the starting blocks. :-)
I used to see them, mostly along the trails through the bracken woods, warming up in the morning sun.
Occasionally I would spot one among the grass on the edge of the woods, usually they would scurry away pretty quick on the approach of a human but on the grass they were much slower and couldn't get the traction they needed to get away.
Why they're are called grass snakes, I don't know, maybe the clour ?
Often found in garden compost heaps, excellent for incubating their eggs.
Have had a couple of large grass snakes in and around my pond. Some while back, a smaller one got trapped in netting covering the pond. Cut around most of the netting and took it into the nearby vets as I wasn’t sure it was a grass snake. They freed it from the netting and I then relocated it back to the pond.