Unknown bird

Today I went back to blipping garden birds through the window, although it has been some time since there was food in the feeders so there were not many birds around.  This bird did visit and I have no idea what it is - or rather I do, but I think it is a young Woodpecker that has not yet become colourful.  It has a black stripe under it's beak and down the back of it's head and markings on its wings and quite large claws to hang on to the feeder.  Perhaps it's a young Magpie; suggestions gratefully accepted.  A second shot in extras.