The Real British X-Files
blakeharris snips from a site called The X-Journals: "Nick Pope used to work for the British Ministry of Defense and for 3 years headed up their UFO project. His remit was to investigate UFO sightings reported to the British government, looking for evidence of any potential threat, or anything judged to be of any 'defence significance.'" Some very interesting anecdotes in here, as well as some background on how certain files about these sightings came to be preserved in the first place.
And the explanation in your particular case is this:
We roll your eyes at yet another made up story. Simple as that.
Why? Because electronic warfare (ELINT) drones like me know how few RADAR systems are actually capable of measuring velocities that high. We also do the math. We sit down with our EW kit and build a real life fingerprint for the specific emitter that 'tracked' this alleged UFO. We tell you that your PRF / PRI, pulse duration, duty cycle, and your cute little pseudo random stagger pattern make your RADAR physically incapable of tracking anything above XXXX knots. We know this beyond any doubt because we have ego's bigger than your average fighter pilot. We know exactly how many pulses per paint it takes to put a little dot on your PPI because we count them, and not just theoretically, we grab a couple of those fighter jocks and have them run a few supersonic passes at the same time. We sit right there next to the scope with you and gloat as we say "I told you so!", pointing fingers at our scrawled out algebra. In terms of 'UFOs', we don't care about little green men, we actually care about "Non allied sucker popping up out of the waves doing mach 2 over our sigint station for some photographs, and then vanishing in a puff of sonic booms to who the hell knows where"
We leave the X file stuff for people back in the MoD, who then retire a couple of years later and hit the lucrative public talk circuits.
When the psych asked me why I wanted to work in a TS security field, I kid you not, I said "because I wanted to know if UFO's really exist" - we both laughed, but I was actually serious :-)