Apologies for coming to this fascinating thread late and for any answers that I may have missed, but (given that the photo in post #19 is clearly a Harrier), could it/they have been Jaguars? The estimable British Aviation Review tells me that on 4th August 1990 2 x Jaguar GR1As visited Newcastle, callsigns Wildcat 1&2. I believe Wildcat was a 226 OCU callsign at the time, which would mean they were likely to have come from Lossiemouth, and Calvine is certainly in the frame for a route from Lossie to Newcastle, especially at low level.
At another level, as a regular traveller on the A9 at that time, frequently at weekends, I cannot believe that the scenario was not witnessed and reported by many other people. Even just the presence of a couple of Harriers/Jaguars/whatever at low level on a Saturday night would be bound to lead to some complaints. So my suspicion is this is all boilleaux. But perhaps there are some ex-226 OCU folks out there who may have some memories of a rare weekend trip to Newcastle?
NS