It was approx. 8cm (3 inches) long, taken at about 10m off the coast of Gozo, near Malta in the Mediterranean last week (early June). He was ever so friendly and I was able to reel off a number of shots; however I thought this was the best one for ID purposes.
Hope someone can help!
Here's another photo from a different angle
A simple Parablennius pilicornis
They are not all yellow, but you can't do a mistake with a yellow blenny in the mediterranean