Although the Kenward stone is considered natural there is another story attributed to it that may give it a prehistoric link. John Chandler has written about it in this Wiltshire Council link....
wiltshire.gov.uk/community/getconcise.php?id=60
which states that the stone had been removed from a field in which other stones lay...
“about 1890, he reported, he had been told by two of Chute’s oldest inhabitants that the stone had been moved there from a field where there were other big stones, some of which had been buried out of the way. But nobody by 1924 could remember where, and so part at least of the pseudo-Kenward stone’s mystery remains.”