Just some musings- I don't think they have a direct bearing on whether the picture is a reflection or not.
I was playing about with a cut-out paper triangle stuck on a fair-sized mirror.
The top half of the diamond in the Calvine photo is very roughly symmetrical with the lower half (midpoint to apex height is approximately the same as midpoint to nadir depth).
If the picture is a reflection, it seems likely that
(1) the surface of the triangle facing us is is roughly perpendicular to the water; or
(2) the photo was taken at a relatively shallow angle. (Or both 1 and 2).
(If the mirror is held with the near edge just below eye level and the far edge angled up slightly, the triangle and its reflection appear to make a symmetrical diamond regardless of whether the triangle is perpendicular to the mirror, is angled towards the observer or angled away from the observer).
If the photo was taken at a shallow angle, we are "seeing" further away towards the top of the picture (when it's the right way up, whichever that is). We don't see a far "shoreline", so it's either a fairly substantial body of water, or quite misty.
(Thinking about it, most of you probably didn't need my picture of a triangle with a folding tab to be stuck on a mirror!)
I'd worked out an elaborate trigonometric proof, but to my surprise a small dog ran in, grabbed it and ran away.
Another possibility is that a fishing line was attached to the model, allowing it to be moved remotely from the shore. Using this method, controlling the exact angle of the model would have been even more challenging.
Yes, I agree- and if the model is partly in the water, the photographer would have to wait for any ripples to subside, and hope no leaf litter/ pond skaters/ midges entered the frame in the interim.
Nothing about this suggests an especially elaborate or well-prepared hoax—rather, it seems like a simple prank designed to fool the local newspaper.
Nit-picking a bit, The Daily Record was Scotland's best-selling daily newspaper (6 days a week) between 1974 and 2006; it's a national (within Scotland) not a local paper, Wikipedia
https://en.wikipedia.org/wiki/Daily_Record_(Scotland).
I agree the picture is probably a hoax.
Whatever effort was put into it, we've got three major threads, this one currently at 23 pages/ 920 posts, and we (collectively) can't even agree what side is up, if there's a jet present, or if we're looking at sky or water! So it's a reasonably effective hoax (IMO

).
The fact that there were six original negatives, not our one picture of a picture, which were at least looked at by RAF / MoD personnel who identified a
second jet, "...probably a Harrier" which was not mentioned by the (claimed) witnesses might indicate a fairly sophisticated hoax.