For what it is worth - probably very, very little - close to Pitlochry is Glen Tilt which amongst the low level aviation fraternity is known as "Star Wars Valley" (not to be confused with Star Wars Canyon in Death Valley),back in the 90's it would probably have seen low level traffic, at least during the week, so perhaps it is not inconceivable that an aircraft could have been spotted there.
Alchad
PS for my money - definitely a harrier in the photo.