Top secret UFO photo finally revealed

"Revealed after 32 years, the top secret picture one MOD insider calls ‘the most spectacular UFO photo ever captured’". This is the title of an article just published in the British paper The Mail.

On August 4, 1990, two young men were working as chefs in a hotel in Pitlochry, a beautiful Highland Perthshire town, just outside the Cairngorms National Park in Scotland.
At 9pm, after a long day in a hot kitchen, they drove about 13 miles north along the A9 to Calvine, a spot on the edge of the Cairngorms, for a walk in the hills.
They hadn’t gone far when they saw a huge, solid, diamond-shaped object, about 100ft long, hovering silently in the sky above them. Terrified, they hid in some bushes and looked up.
Minutes later, they heard the scream of a jet aircraft going north: In 1990, RAF Leuchars in Fife had two squadrons of Tornado fighters on 24-hour standby to intercept Russian intruder aircraft.
The jet came back and circled the ‘thing’ before heading off on its original course, as if the pilot had seen the object too and had come back for a closer look.
Eventually the two men stuck their camera out from where they were hiding and fired off six frames. At that point, the object shot vertically upwards and disappeared way, way up in to the sky.
Convinced they’d just seen a UFO, they took their photos to the Daily Record, one of Scotland’s leading newspapers. But no story was ever printed: The paper passed the pictures on to the Ministry of Defence.

The article writer, David Clarke, devoted a lot of time in recent years to attempt to dig up that photo, and he finally succeeded, in the desk drawer of an 83 year old retired RAF officer no longer concerned about official secrets acts. 

Clarke thinks it was a top-secret US experimental aircraft, but I'm very skeptical of that for many reasons, especially because of the object's very rapid vertical maneuver and other extraordinary behavior reported by the two witnesses, when it simply and suddenly shot upwards out of sight in the sky. A 100-foot long aircraft just doesn't do that, for a host of aerodynamic and inertial reasons. And a 100-foot long aircraft doesn't silently hover in the sky, either. These performances are way beyond the fundamental aerodynamic and inertial limitations of all known aircraft technology, especially propulsion.

More on the Calvine Scotland UFO.

From a 2012 article by Nick Pope (who ran the British MOD UFO office for years):

I first came across this story in 1991, when I joined the UFO project. A poster-sized enlargement of the best photo was prominently displayed on the office wall. I worked in a four-person office where my predecessor had put it up. It was one of the few visible UFO-related items on display; most stuff was locked away.....Sometimes, people would come to our office to discuss non-UFO business and some of these people weren’t aware that the UFO project was embedded in the section. You’d have this surreal moment when they’d stop mid-sentence, stare at it, point and say “what the hell’s that?” – this wasn’t the archetypal distant, blurred UFO photo. This was up close and personal, reach out and you can touch it stuff. “I don’t know what it is, but it’s not one of ours” was our stock answer to the inevitable question.
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I asked my Defence Intelligence Staff (DIS) opposite number about the image. I was told that the official assessment was that the photos were real and the craft had a diameter of around 25 metres (over 80 feet). At one particularly surreal briefing on the UFO phenomenon my DIS opposite number indicated the photo and pointed his finger to the right: “It’s not the Americans”, he said, before pointing to the left and saying “and it’s not the Russians”. There was a pause, before he concluded “and that only leaves …” - his voice trailed off and he didn’t complete the sentence, but his finger was pointing directly upwards
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So why the MoD interest and secrecy? Though we’d never say so publicly, the bottom line was that we wanted the technology. We were interested in UFO photos such as these in case they could tell us something about propulsion systems, energy sources, avionics systems, aerodynamics, etc. There was a running joke that we didn’t care if a craft such as the one shown in the Calvine UFO photo was American, Russian or Martian – all we knew was that it was better than anything we had and that we wanted the technology for our own military aircraft and drones.

A possible most likely hypothesis about the Calvine UFO:

Contrary to the ETI hypothesis, it is true that the (probably Harrier) jet that circled the object briefly then went on its way didn't behave as you would think it would if the craft was a totally unknown possibly alien vehicle, more like it was an experimental cold war lighter than air surveillance vehicle. If it was alien and probably ET, there would have been a swarm of Harriers coming up close, doing a lot of photography, etc., or even attacking it. However, the experimental lighter than air cold war surveillance vehicle idea to be true would require throwing out the witnesses' statement that the UFO suddenly zoomed up into the sky and disappeared in a momemt. No Earth technology could acheive that. So the witnesses had to be lying about that. Why? And then what about their other statements - were they lies too? 

However, another scenario suggests itself - that there was or is a beyond top secret agreement between the authorities in Britain and the US, and the ETs, for some sort of mutual cooperation for various reasons, one of which could be to avoid inadvertent conflicts, which obviously would be disastrous for the human forces. This latter scenario would explain most or all of the features of this sighting without requiring us to throw out any of the witnesses' statements. It would just require one subsidiary hypothesis, that this hypothesized ET/human agreement is being kept secret even from most levels of the governments on both sides. Hence the apparent ignorance of the British MOD authorities in their half-hearted "investigation" of UFOs carried out over a number of years, even to the point of their apparently considering the Calvine UFO photograph to be maybe an authentic unknown manufactured craft. That seems plausible to me. Such a hypothesized agreement might also cover the authorities not challenging and interfering with the mass phenomenon of the cattle mutilations probably carried out for years by the ETIs to deeply analyze our biology without interfering in any major way with our society.

I prefer the above scenario, but there seems to be at least one more possible hypothesis, related to the above: that the apparently alien craft was an experimental British or more likely US vehicle incorporating antigravity/inertia nullifying technology reverse engineered from crashed UFOs. I think this is much more unlikely for the reasons discussed elsewhere, mainly that we would expect there to have been major impacts to our mainstream technology infrastructure, impacts that haven't occured.