The holed stone is reckoned to be the closing section of a long barrow-like structure. There are fairly intact ones in France, I believe. There was a carved stopper that fit in the hole to keep it closed. Made of stone. I own one of these stopper stones - a bung - but it has lost its hole. (I guess the rest of the structure was quarried in the 1700's when a roadbridge was being built). It'd be too much to suppose that yr holed stone and my stopper were the same size - if they were it might be good to put them together (sometime) ...