As several have commented it is a nice change to see a sensible debate.
I have seen two things while aviating that I could not identify or explain at the time. One in 1963 was at height over the Boscombe area and looked like a very high level dot of an aircraft that exploded as I was looking at it. (I was at 40k and it was way above me) after which I saw debris falling on my port side. The other passed beneath me in 1954. I first saw it out on the starb side, it tracked under our RAE Lincoln and reappeared out the port side (we were about 12k) I shouted as I moved to look out the port side but nobody else in the crew saw it. I couldn’t guess how far it was below us because I didn’t know the size … but since it took a mo to appear out the other side I suspect it was fairly well below. We were over West Freugh range and dropping prototype cluster bombs from height. Range radar was calling the release. They saw nothing.
I reported both events. Both were investigated by ATC. The first was explained as the bursting of a high altitude trials balloon from Larkhill at approx 90k. The debris I saw was thought to be part of an instrumentation package.
Nobody had anything to offer regarding the West Freugh event, despite it getting people’s attention from a range safety standpoint. The shape of what I saw was best described as the front view of a Vulcan if you remove the fin. Or, if you prefer, a sphere with a couple of cones out either side where the base diameter of the cones was say 90% of the diameter of the sphere. The tips of the cones were slightly rounded. It was of uniform dark colour with no details visible, travelling one cone tip first. IF my impression that is was well below us was correct it must have been doing say 250 kts. It was broad daylight. I had my leg pulled a bit by some in the mess (we were visitors for a couple of days) but not by those in the crew who knew me.