Most snakes are quite rare to find in this country,I've only ever seen 3 in all my life of having been in the countryside most days.
But this morning my cocker bitch that can find the only nest of mice in a ten acre field found a grass snake that was at least 1.5/ 2 metres long! My dog just stood and barked at it, until it just slithered of and disappeared from sight within yard of being seen.
seem,s to be quiet a few round here they only seem to come out on sunny days, no seen any long ones but the ones round here are more brownish black with nice diamond patterns, they are very timid and slither away quickly.
your second link is better, hard to say a mix between the two, the they are near water might be the grass snake, saw the slow worm pic on the link not seen one since i was a schoolboy used to catch them on hounslow heath.
in the rubbish heap at the bottom of my garden. I don't visit that part of the garden that often, and was amazed to see a fully grown female going full tilt back into the depths of the heap as I approached. She had obviously been sunbathing, and I startled her. She wasn't 2 metres long - I would estimate just over a metre. Snakes can often look bigger than they really are.
Later that month I saw two or three much smaller snakes, which I took to be her babies.