"When Stuart Piggott and his team of excavators from the Royal Commissiom on Ancient Monuments began digging a neolithic period oval shaped barrow on Thickthorn down, above Gussage St Michael in the foothills of Cranborne chase, they were constantly asked if they had yet discovered the golden coffin. Not only was there no gold, however, but Piggott's excavation in 1933 found nothing else either of what should have been the primary interments in the 5,000 year old mound.
The barrow may have been the cenotaph for a warrior who was killed elsewhere. All that was left by the original builders were a couple of chalk-cut phallic objects which were found in the lowest layer of silting in the ditch which surrounded the mound. Hundreds of years later the mound had been dug into and re-used for three other burials. Piggott and the locals were equally puzzled that it had been built to cover nothing whatever; the story of the golden coffin stuck tenaciously until the site had been completely cleared. the mound was reconstructed after the excavation had finished."
From Mysterious Dorset by Rodney Legg.
This is very similar to the story about Cowleaze barrows near Milborne St Andrew, minus the lightning.