The Reverend James Raine (who edited the memoirs mentioned below) didn’t want to go for the Druidic explanation, and dug out a copy of the Newcastle Courant of 9 October 1725 in an effort to dispel the myth:
It appears from this authority that upon the marriage of Sir William Blackett (a while before) “Shaftoe Vaughan, Esq. caused Shafto Craggs to be illuminated in the night,” and “a large Punch Bowl was cut in the most elevated rock, which was filled with such generous liquor as was more than sufficient for the vast crowd of neighbouring inhabitants,” &c.
As far as I’m concerned it’s the ‘a while before’ that gives this away – sounds like just another folklorey explanation for the ‘Punch Bowl’ if you ask me.