Failed to spot this one. I drove up to the entrance of the power station and then had a choice of going left (staff only) or right (visitors parking) - I didn't feel comfortable doing either. As you would expect there were plenty of police vehicles about. I looked along the security fence as far as I could but did not spot the stone. Looking at the phot it looks like the stone is around the other side of the site? Don't know how you wuld access that section?
Bad 'vibes' so I left.
Your post made me think, Carl. Maybe this stone is the one that features in the folklore about Wibdon Broad Stone about a stone throwing contest (which is where Ike's thought should have led me before).