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Confidence: I'm as sure as I can be.
Aka Long spined sea scorpion.
Easily confused with Myoxocephalus scorpius but both small white fleshy barbels can be seen in the photo, sticking out from the rear edge of the maxillary, near the rear of the eyes, at the sides of the head.
These are absent on M. scorpius.
This is Taurulus bubalis and its a nicely coloured one, they do change colour quite quickly when moved over a new surface. Eg this one would very likely turn a buff/grey mottling if moved over sand. 2 tone ones like this can go totally monochrome also.
Edit- changed original post, I said rear of head, should have said rear of the eyes, sorry about that! Tiny white barbels virtually below the eyes, slightly to the rear of them.
Lat/Lng: 50.156, -5.0711
OS grid ref: SW807329