Heddwen wrote:I BELIEVE that these are good sources:
The Pagan Religions of the Ancient British Isles by Dr R Hutton
The White Goddess by Robert Graves, Faber
Sadly though valuable in a poetic sense the White Goddess is far from being a useful source factually and is misleading on occasion.
Regarding Celtic creation myth I agree with the consensus, there is no early source. However Germanic sources might be of interest, as might Greek. I like the Finnish creation myth very much, one version of which you can find in the Kalevala. http://www.sacred-texts.com/neu/kveng/kvrune01.htm
There is an unfashionable but persistent theory that the Picts were a Finno Ugric people in which case the earliest Finnish mythology may have been quite similar to some Celtic stuff we have lost.