The Data Protection Act specifically allows the publication of names, etc where such information may be 'in the public interest'.
"In the public interest" is not "what interests some members of the public".
The files were released by the National Archives c. 2011 IIRC. Almost all (maybe all, full stop) names and addresses of claimants have been redacted.
Copies of DEFE 24/1940/1, DEFE 24/1940/2 and DEFE 31/180/1 attached below; have a quick look.
The National Archives probably have competent legal advice.
It is patently absurd for the perpetrators of this event to try to claim anonymity 35 years later. The event itself is widely publicised.
If they're actively trying to maintain their anonymity, it's working, so it's not absurd.
The claimant(s) might not be aware that there is continued interest in the Calvine photo- we have no reason to believe that they had a prior interest in UFOs, and if their story is a hoax, it was turned down in 1990, so they wouldn't have any reason to develop an interest in UFOs (which "real" witnesses might). It seems unlikely they live in the Calvine/ Pitlochry area.
Unless they were regular
Sun readers, or like TV shows/ internet stuff about UFOs, they could be totally oblivious.
If a claimant is aware of ongoing interest, they might have their own reasons to leave it buried in the past; perhaps they have a job where perceived honesty is even more significant than it is normally held to be. Maybe there are other things about that time in their lives that they don't want to revisit. Or they're not very well informed, and genuinely fear getting into trouble with "the authorities". Or, for whatever other reason, they don't want media attention.
Of course, as a young man/ young men, if they ever did any hitchhiking along the A9 they might have been abducted by an alien driving a small red Toyota (the A9 is a hunting ground for the female alien Isserley in Michel Faber's novel
Under the Skin, 2000,
https://en.wikipedia.org/wiki/Under_the_Skin_(novel); disturbing but compelling).
