Slavonian Grebe (Podiceps auritus), Wilstone Reservoir, Nr Tring, Hertfordshire, 27/10/2012. Highlighting the beak shape and markings (conclusively ruling out Black-necked Grebe, which would be the other contender locally). Of note, the pale tip. Also of note, the pale patch of feathers between the eye and beak laterally and nice white cheeks.