Considering its age and fame, very little folklore seems to exist. The only reference I can find is that the ghost of a priest enters the barrow at sunrise on Midsummer Day followed by a ghostly white dog with red ears, which is pretty similar to what Rhiannon found.
Just been trawling Google as I remembered a somewhat strange incident when I visited West Kennet Longbarrow on April 12th 1999 not long before sunset.
After crossing the beck at the botom of the slope and on to the narrow path up to the Barrow my brother-in-law and I saw a light coloured dog coming towards us down the path. If you have been you will know that it isn't wide, single file. So as the dog, which was quite a size, bit like a white greyhound only bigger, ran towards us we stod aside. I actually tried to climb into the field, well you never know, it could have been after my legs. However, it wasn't, and ran right past, not even acknowledging our existence. We both then turned to see that it had gone and there was no sign of it. Not on the path or in the fields on either side. It looked as if it had disappeared.
I'm not the type of person who thinks ghosts etc exist and there is probably an explanation for his/her disappearance immediatly behind us, but it just didn't seem right. The dog literally disappeared. Before anyone suggests, we were both totally sober in all forms, having driven from Devizes.
Anyone else seen anything? I know I'm not going mad!
That's very nice, that's a good fortean story. I rather hope it really was a mysterious otherworldly greyhound. Even if it was the type that wasn't really there but still looked real so made you get out the way (that's one way you can sort of rationalise your way out of it if you want to!)
(meanwhile, I have been driving myself mad not knowing and not being able to find where the folklore story I so casually added comes from originally. Grrr.)