Hi Per-Gunnar- This is a 1st winter Black-headed Gull, Larus ridibundus. This young bird has not developed the dark hood yet and adults lose it in the winter anyway. All you see is remnants of grey behind the eye. It's a 1st winter bird for several reasons including the bill colour (adults would have a reddish bill) and the dark band at the end of the tail (adults would have a white tail). A winter Common Gull would have dusky along the sides of the breast, dusky head (no gray patches like this one), and different coloured bill and feet.