Hi ellie:
You mention that you were "advised" about a Police caution you received in 1992. Who told you this?
In any case, a formal Police caution should not have existed 5 years after it was given. Although a caution did not constitute a conviction, it had the effect of creating a criminal record which, within that 5 year period, could have been used against you.
Even as far back as 1992, the "norm" would have meant someone attending a Police Station(if a juvenile, with parent or appropriate adult), having an allegation put to you in an interview under caution, or even under arrest, admitting the offence, then receiving a written form which you had to sign to say that you accepted the caution.
The documentation would all have been kept at that Police Station. However, you haven't given any details whatsoever about why you may have been cautioned and I'm therefore unable to advise you further.