Slavonian Grebe at Scammonden 28/01/13

I don't mind admitting to anyone that the identification of a small black and white grebe first seen by my brother Stephen earlier on today at Scammonden has caused me a few problems, not least as I wasn't able to obtain even half-decent views of it until turned 3pm when the weather conditions were horrendous. In the field or on the water so to speak it was very difficult to ignore two id features which would have lead to it being two different species. It was obvious that it was either a Slavonian Grebe or a Black-necked Grebe and having seen both species previously in winter plumage I felt that I should have been able to determine which one I was looking at but to be perfectly truthful I simply could not. Fair enough it is a small bird, Scammonden is a fairly large body of water, it wasn't easy to find it initially never mind get remotely close to it, the weather was arguably as bad as it could have been, horizontal rain, choppy water, gale force winds making it difficult to hold the scope steady and diminishing light, but having said all that I was sure I could see that this grebe had a clear demarcation between its black head and clean white cheeks, pointing to Slavonian Grebe, however this grebe appeared to have as far as I could make out quite a dark grey collar normally associated with Black-necked Grebe. I am sure most birders if they are honest will have experienced a similar mixture of emotions in a situation such as this, embarrassment, annoyance, even ineptitude, however whilst I observed this bird it spent the majority of the time diving and more often than not catching tiny fish, therefore I couldn't discern to my frustration the shape of its bill or even head shape, my 30x kowa eyepiece in this light and conditions or maybe my eyes or expertise just did not seem up to the mark sadly. I felt my only salvation would be to go into stealth mode and therefore basically crept along the east embankment on all fours getting rather wet, fortunately the weather was that bad that even dog walkers had disappeared therefore I am not aware of anyone actually witnessing me stalking this little bird, however I eventually managed to get close enough to it to hopefully prove that we have a Slavonian Grebe in our midst, although I am still puzzled by the dark collar which may be due to the poor light or possibly oiling? I hope that it hangs around long enough for any local birder to see it, hopefully in more favourable light and weather conditions! First photo, pale tip to the bill on this photo is apparent

Second one highlighting the troublesome dark collar

Third one showing flat crown peaking at the rear

Finally the last one showing dark plumage or oiling on its chin which really added to the confusion as far as I was concerned. On a positive note it had just caught another small fish, anyone know what species of fish are in Scammonden?