An Unusual House Guest

Had an intriguing visitor in our front room last night, a little common lizard sat on the slate floor. I didn't see him myself(although I have several times before and once nearly stood on him in the dark!) but my wife did. She watched him for a while but didn't fancy the idea of picking him up and taking him outside so he eventually sneaked under our sofa and vanished. As far as we know he's still under there, so we await his next visit...