Riding along today on a back country road I see a length of wire or pipe in the road and think " I dont want to run over that only on passing do I realise its a snake about 3 foot long - and that was bendy snake shape, I turned around and went back so I could grab him and get a photo but he had gone.
If it was an indigenous snake and not a escaped pet one it would have been a grass snake, not poisonous but you still need to be careful with the buggers cos the spit foul smelling stuff to warn off would be attackers, and contrary to some peoples beliefs they will bite you.
I worked on the building sites for many years and came across a number of snakes both Adders (Vipers) and Grass snakes, Adders rarely go more than 18 inches long the female is the bigger of the two. Grass snake can, but not often reach 6 foot in length, (Very Rare) the longest I have seen was about 3 foot 6 inches long and I would not have wanted that bugger to bite me, it did spit at me thankfully missed but the stench nearly made me puke, the infamous builder shovel put paid to that sod, again the female are the larger of the species.
Grass snake are not poisonous but neither is a rat but both would make you feel very poorly for a day or two and you might get a localised infection on the would site.
I feel you are talking about a relative when I saw the title of your post Sharpie, well if he was gone when you got back to the spot he was also a racing snake.