please help us identify a snake we've just come across

[Sixer]

We live in North Somerset. We have just come back from our dog walk, after discovering a little snake. Another walker stopped to see what we were up to. Standing well back, the other person decided it was a baby adder, and we should stay well away. Obviously slithered from a nest (there's more!).
I have goggled adder so far, and it's nothing like we saw.
Our snake was about 6 ins, blackish with diamond markings on the side. A very yellow diamond on the back of it's head/neck.
Any ideas anyone. The DC are here with me, wondering and very interested.

Sounds more like a grass snake - but you can't be too careful, so generally avoid i suppose. Have you tried google images?

Grass snake?

You stopped to look at it!!!!!!

OTOH - grass snakes are more green with diamond pattern, adders are darker, can be blackish, but have zig zags, not diamonds. so - a bit confusing.

I'm still goggling and haven't found anything like it yet.
We had to stop to look, I thought it might have been a sloe worm to show the boys. Then realised NOP, put the dog on the lead, then watched from a safe distance. (about 3 foot between him and us).

oh, now i'm not clear, It was small, and at the distance and really can't be sure now if it was diamonds or zig zags.. There was this really yellow diamond on the back of it. I'm quite sure i'd know it if I saw it again. Still trawling pics.

Grass snake's yellow collar

Thanks for the link. It's not it though. Even DC are saying no. It was dark, nearly black in colour. which is why it is also hard to say for sure what pattern was on it. we are trawling through the link though. I also noticed the young grass snakes don't appear until Juneish, whilst the adders appear early spring. Saying that, it doesn't even look like the adders. we'll keep looking!!

Sorry my mistake, little Grass snakes appear in Autumn. Not June thats when eggs are laid