The secrecy about the location is just bloody-mindedness on the part of the photographer and his friend.
He photographed a bird that he thought was a juvenile marsh harrier (true) and asked on a Facebook site for confirmation of his ID. He told his friend the location and further photos were taken and posted.
He is a photographer who has a pretty low opinion of birders from his comments on that site and is refusing to disclose the location as a dig at birders. He and a few others came in for a bit of flak earlier this year for swamping a local site on a daily basis, where a barn owl was breeding and providing good photo ops on its daytime hunting forays. The photographers, who were not birders, had to be warned about encroaching on the breeding barn and standing on the flight line of the returning owl to get shots with prey. He is now taking the opportunity to get back at birders who he feels spoiled his fun.
That' my interpretation of the situation, anyway.
At first he was even refusing to report the sighting to the county recorder, but I believe from further comments on that Facebook site that he is inclined to report it. For further info go to Northumberland Wildlife on Facebook and prepare to be amazed.