As with you my gut feeling was common lizard. agree an unusually marked one, I resorted to Arnold, Burton and Ovenden for help.

Something the book refers to which I admit I had never noticed is that sand lizards have a series of very narrow scales down the centre of the back and that the scales on the back of a common lizard are slightly keeled.

If you look closely at the scales on your very clear photo the scales on the rear half of the back, especially, are keeled. I checked this on a few more common lizard photos on iSpot, something you can do very easily with the new layout, and they too have keeled scales on the back.

If you then look at some of the sand lizards on iSpot they have very narrow scales down the centre of the back and larger ones to the side. Unlike common lizard where the scales are a more uniform size over the whole body. I guess I just have not looked so closely before, they don't usually hang around long enough! You live and learn.